Issue #20443 has been updated by byroot (Jean Boussier). File Capture d’écran 2024-04-22 à 18.41.52.png added To add a little bit more context on @eightbitraptor's description. In some graph you see 3 groups: - `oobgc-off`: which is workers without any Out of Band GC. - `oobgc-on`: which is workers with our previous OOB GC implementation (once every 128 to 512 requests, 20% more every time) - `oobgc-disable-major`: which is the new OOB GC implementation that only run GC when `GC.need_major?` returns true. The new implementation not only improve latency in most case, it also reduce the capacity impact of having workers running major GC when it wasn't needed. Here is the graph of `GC.stat[:major_gc_count]` over these 3 groups, and as you can see `oobgc-disable-major` runs major GC only about as often as no-OOBGC, whereas the previous implementation is triggering more often than actually needed, wasting server capacity.  ---------------------------------------- Feature #20443: Allow Major GC's to be disabled https://bugs.ruby-lang.org/issues/20443#change-108055 * Author: eightbitraptor (Matthew Valentine-House) * Status: Open ---------------------------------------- [[Github PR #10598]](https://github.com/ruby/ruby/pull/10598) ## Background Ruby's GC running during Rails requests can have negative impacts on currently running requests, causing applications to have high tail-latency. A technique to mitigate this high tail-latency is Out-of-band GC (OOBGC). This is basically where the application is run with GC disabled, and then GC is explicitly started after each request, or when no requests are in progress. This can reduce the tail latency, but also introduces problems of its own. Long GC pauses after each request reduce throughput. This is more pronounced on threading servers like Puma because all the threads have to finish processing user requests and be "paused" before OOBGC can be triggered. This throughput decrease happens for a couple of reasons: 1. There are few heuristics available for users to determine when GC should run, this means that in OOBGC scenarios, it's possible that major GC's are being run more than necessary. 2. The lack of any GC during a request means that lots of garbage objects have been created and not cleaned up, so the process is using more memory than it should - requiring major GC's run as part of OOBGC to do more work and therefore take more time. This ticket attempts to address these issues by: 1. Provide `GC.disable_major` and its antonym `GC.enable_major` to disable and enable only major GC 2. Provide `GC.needs_major?` as a basic heuristic allowing users to tell when Ruby should run a Major GC. These ideas were originally proposed by @ko1 and @byroot in [this rails issue](https://github.com/rails/rails/issues/50449) Disabling GC major's would still allow minor GC's to run during the request, avoiding the ballooning memory usage caused by not running GC at all, and reducing the time that a major takes when we do run it, because the nursery objects have been cleaned up during the request already so there is less work for a major GC to do. This can be used in combination with `GC.needs_major?` to selectively run an OOBGC only when necessary ## Implementation This PR adds 3 new methods to the `GC` module - `GC.disable_major` This prevents major GC's from running automatically. It does not restrict minors. When `objspace->rgengc.need_major_gc` is set and a GC is run, instead of running a major, new heap pages will be allocated and a minor run instead. `objspace->rgengc.need_major_gc` will remain set until a major is manually run. If a major is not manually run then the process will eventually run out of memory. When major GC's are disabled, object promotion is disabled. That is, no objects will increment their ages during a minor GC. This is to attempt to minimise heap growth during the period between major GC's, by restricting the number of old-gen objects that will remain unconsidered by the GC until the next major. When `GC.start` is run, then major GC's will be enabled, a GC triggered with the options passed to `GC.start`, and then `disable_major` will be set to the state it was in before `GC.start` was called. - `GC.enable_major` This simply unsets the bit preventing major GC's. This will revert the GC to normal generational behaviour. Everything behaves as default again. - `GC.needs_major?` This exposes the value of `objspace->rgengc.need_major_gc` to the user level API. This is already exposed in `GC.latest_gc_info[:need_major_by]` but I felt that a simpler interface would make this easier to use and result in more readable code. eg. ```ruby out_of_band do GC.start if GC.needs_major? end ``` Because object aging is disabled when majors are disabled it is recommended to use this in conjunction with `Process.warmup`, which will prepare the heap by running a major GC, compacting the heap, and promoting every remaining object to old-gen. This ensures that minor GC's are running over the smallets possible set of young objects when `GC.disable_major` is true. ## Benchmarks We ran some tests in production on Shopify's core monolith over a weekend and found that: **Mean time spent in GC, as well as p99.9 and p99.99 GC times are all improved.** <img width="1000" alt="Screenshot 2024-04-22 at 16 41 49" src="https://github.com/ruby/ruby/assets/31869/6cff5b11-2e21-40c1-bb84-d994e0e1798d"> **p99 GC time is slightly higher.** <img width="1000" alt="Screenshot 2024-04-22 at 16 44 55" src="https://github.com/ruby/ruby/assets/31869/dc645cbe-9495-46f0-8485-24e790c42f32"> We're running far fewer OOBGC major GC's now that we have `GC.needs_major?` than we were before, and we believe that this is contributing to a slightly increased number of minor GC's. raising the p99 slightly. **App response times are all improved** We see a 9% reduction in average and p99 response times when compared against standard GC (4% p99.9 and p99.99). <img width="1000" alt="Screenshot 2024-04-22 at 16 55 53" src="https://github.com/ruby/ruby/assets/31869/8a80c102-1564-4bc9-ba44-6e9a8b85f971"> This drops slightly to an 8% reduction in average and p99 response times when compared against standard OOBGC (3.59 p99.9 and 4% p99.99) <img width="1000" alt="Screenshot 2024-04-22 at 16 56 10" src="https://github.com/ruby/ruby/assets/31869/1baef7ea-0155-4ff9-8ba4-a967b75749fe"> ---Files-------------------------------- Capture d’écran 2024-04-22 à 18.41.52.png (279 KB) -- https://bugs.ruby-lang.org/

Issue #20443 has been updated by eightbitraptor (Matthew Valentine-House). nateberkopec (Nate Berkopec) wrote in #note-4:

Regarding the interface:

``` ruby GC.disable(major: true) GC.disable(type: :major) ```

Should we consider these additional keyword arguments rather than adding a new method?

I slightly prefer having a new method pair for this, however I don't object to changing it. I do have a slight concern that `GC.disable(major: true)` could be read either as disabling major GC's or keeping majors enabled and disabling minors So if we decide to use the keyword approach I prefer `GC.disable(type: major)` ---------------------------------------- Feature #20443: Allow Major GC's to be disabled https://bugs.ruby-lang.org/issues/20443#change-108086 * Author: eightbitraptor (Matthew Valentine-House) * Status: Open ---------------------------------------- [[Github PR #10598]](https://github.com/ruby/ruby/pull/10598) ## Background Ruby's GC running during Rails requests can have negative impacts on currently running requests, causing applications to have high tail-latency. A technique to mitigate this high tail-latency is Out-of-band GC (OOBGC). This is basically where the application is run with GC disabled, and then GC is explicitly started after each request, or when no requests are in progress. This can reduce the tail latency, but also introduces problems of its own. Long GC pauses after each request reduce throughput. This is more pronounced on threading servers like Puma because all the threads have to finish processing user requests and be "paused" before OOBGC can be triggered. This throughput decrease happens for a couple of reasons: 1. There are few heuristics available for users to determine when GC should run, this means that in OOBGC scenarios, it's possible that major GC's are being run more than necessary. 2. The lack of any GC during a request means that lots of garbage objects have been created and not cleaned up, so the process is using more memory than it should - requiring major GC's run as part of OOBGC to do more work and therefore take more time. This ticket attempts to address these issues by: 1. Provide `GC.disable_major` and its antonym `GC.enable_major` to disable and enable only major GC 2. Provide `GC.needs_major?` as a basic heuristic allowing users to tell when Ruby should run a Major GC. These ideas were originally proposed by @ko1 and @byroot in [this rails issue](https://github.com/rails/rails/issues/50449) Disabling GC major's would still allow minor GC's to run during the request, avoiding the ballooning memory usage caused by not running GC at all, and reducing the time that a major takes when we do run it, because the nursery objects have been cleaned up during the request already so there is less work for a major GC to do. This can be used in combination with `GC.needs_major?` to selectively run an OOBGC only when necessary ## Implementation This PR adds 3 new methods to the `GC` module - `GC.disable_major` This prevents major GC's from running automatically. It does not restrict minors. When `objspace->rgengc.need_major_gc` is set and a GC is run, instead of running a major, new heap pages will be allocated and a minor run instead. `objspace->rgengc.need_major_gc` will remain set until a major is manually run. If a major is not manually run then the process will eventually run out of memory. When major GC's are disabled, object promotion is disabled. That is, no objects will increment their ages during a minor GC. This is to attempt to minimise heap growth during the period between major GC's, by restricting the number of old-gen objects that will remain unconsidered by the GC until the next major. When `GC.start` is run, then major GC's will be enabled, a GC triggered with the options passed to `GC.start`, and then `disable_major` will be set to the state it was in before `GC.start` was called. - `GC.enable_major` This simply unsets the bit preventing major GC's. This will revert the GC to normal generational behaviour. Everything behaves as default again. - `GC.needs_major?` This exposes the value of `objspace->rgengc.need_major_gc` to the user level API. This is already exposed in `GC.latest_gc_info[:need_major_by]` but I felt that a simpler interface would make this easier to use and result in more readable code. eg. ``` out_of_band do GC.start if GC.needs_major? end ``` Because object aging is disabled when majors are disabled it is recommended to use this in conjunction with `Process.warmup`, which will prepare the heap by running a major GC, compacting the heap, and promoting every remaining object to old-gen. This ensures that minor GC's are running over the smallets possible set of young objects when `GC.disable_major` is true. ## Benchmarks We ran some tests in production on Shopify's core monolith over a weekend and found that: **Mean time spent in GC, as well as p99.9 and p99.99 GC times are all improved.** <img width="1000" alt="Screenshot 2024-04-22 at 16 41 49" src="https://github.com/ruby/ruby/assets/31869/6cff5b11-2e21-40c1-bb84-d994e0e1798d"> **p99 GC time is slightly higher.** <img width="1000" alt="Screenshot 2024-04-22 at 16 44 55" src="https://github.com/ruby/ruby/assets/31869/dc645cbe-9495-46f0-8485-24e790c42f32"> We're running far fewer OOBGC major GC's now that we have `GC.needs_major?` than we were before, and we believe that this is contributing to a slightly increased number of minor GC's. raising the p99 slightly. **App response times are all improved** We see a ~2% reduction in average response times when compared againststandard GC (~7% p99, ~3% p99.9 and ~4% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 17" src="https://gist.github.com/assets/31869/70e81fa5-77b2-469a-8945-88bf8f8fefe9"> This drops slightly to an a ~1% reduction in average response times when compared against our normal OOBGC approach (~6% p99, ~2% p99.9 and ~3% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 29" src="https://gist.github.com/assets/31869/cbaa3807-0cd1-4dba-a5e6-b9df91024d73"> EDIT: to correct a formula error in the original Average charts, numbers updated. ---Files-------------------------------- Capture d’écran 2024-04-22 à 18.41.52.png (279 KB) -- https://bugs.ruby-lang.org/

Issue #20443 has been updated by shan (Shannon Skipper). I wonder if "full_sweep" be worth considering as an alternative to "major" to align with the existing `GC.start(full_sweep: true)` keyword argument? Or they could be aliased, but it seems nice to be consistent if I'm understanding it correctly that they have equivalent meaning. ``` ruby GC.start(full_sweep: true) # existing default GC.enable_full_sweep GC.disable_full_sweep ``` or would a setter make sense? ```ruby GC.full_sweep? #=> true GC.full_sweep = false GC.full_sweep? #=> false ``` For checking if a full sweep or major is needed, would the addressing the Object convention mean `GC.need_full_sweep?` singular, `Dir.exist?` style? Or a plain `GC.full_sweep?` seems nice. ---------------------------------------- Feature #20443: Allow Major GC's to be disabled https://bugs.ruby-lang.org/issues/20443#change-108096 * Author: eightbitraptor (Matthew Valentine-House) * Status: Open ---------------------------------------- [[Github PR #10598]](https://github.com/ruby/ruby/pull/10598) ## Background Ruby's GC running during Rails requests can have negative impacts on currently running requests, causing applications to have high tail-latency. A technique to mitigate this high tail-latency is Out-of-band GC (OOBGC). This is basically where the application is run with GC disabled, and then GC is explicitly started after each request, or when no requests are in progress. This can reduce the tail latency, but also introduces problems of its own. Long GC pauses after each request reduce throughput. This is more pronounced on threading servers like Puma because all the threads have to finish processing user requests and be "paused" before OOBGC can be triggered. This throughput decrease happens for a couple of reasons: 1. There are few heuristics available for users to determine when GC should run, this means that in OOBGC scenarios, it's possible that major GC's are being run more than necessary. 2. The lack of any GC during a request means that lots of garbage objects have been created and not cleaned up, so the process is using more memory than it should - requiring major GC's run as part of OOBGC to do more work and therefore take more time. This ticket attempts to address these issues by: 1. Provide `GC.disable_major` and its antonym `GC.enable_major` to disable and enable only major GC 2. Provide `GC.needs_major?` as a basic heuristic allowing users to tell when Ruby should run a Major GC. These ideas were originally proposed by @ko1 and @byroot in [this rails issue](https://github.com/rails/rails/issues/50449) Disabling GC major's would still allow minor GC's to run during the request, avoiding the ballooning memory usage caused by not running GC at all, and reducing the time that a major takes when we do run it, because the nursery objects have been cleaned up during the request already so there is less work for a major GC to do. This can be used in combination with `GC.needs_major?` to selectively run an OOBGC only when necessary ## Implementation This PR adds 3 new methods to the `GC` module - `GC.disable_major` This prevents major GC's from running automatically. It does not restrict minors. When `objspace->rgengc.need_major_gc` is set and a GC is run, instead of running a major, new heap pages will be allocated and a minor run instead. `objspace->rgengc.need_major_gc` will remain set until a major is manually run. If a major is not manually run then the process will eventually run out of memory. When major GC's are disabled, object promotion is disabled. That is, no objects will increment their ages during a minor GC. This is to attempt to minimise heap growth during the period between major GC's, by restricting the number of old-gen objects that will remain unconsidered by the GC until the next major. When `GC.start` is run, then major GC's will be enabled, a GC triggered with the options passed to `GC.start`, and then `disable_major` will be set to the state it was in before `GC.start` was called. - `GC.enable_major` This simply unsets the bit preventing major GC's. This will revert the GC to normal generational behaviour. Everything behaves as default again. - `GC.needs_major?` This exposes the value of `objspace->rgengc.need_major_gc` to the user level API. This is already exposed in `GC.latest_gc_info[:need_major_by]` but I felt that a simpler interface would make this easier to use and result in more readable code. eg. ``` out_of_band do GC.start if GC.needs_major? end ``` Because object aging is disabled when majors are disabled it is recommended to use this in conjunction with `Process.warmup`, which will prepare the heap by running a major GC, compacting the heap, and promoting every remaining object to old-gen. This ensures that minor GC's are running over the smallets possible set of young objects when `GC.disable_major` is true. ## Benchmarks We ran some tests in production on Shopify's core monolith over a weekend and found that: **Mean time spent in GC, as well as p99.9 and p99.99 GC times are all improved.** <img width="1000" alt="Screenshot 2024-04-22 at 16 41 49" src="https://github.com/ruby/ruby/assets/31869/6cff5b11-2e21-40c1-bb84-d994e0e1798d"> **p99 GC time is slightly higher.** <img width="1000" alt="Screenshot 2024-04-22 at 16 44 55" src="https://github.com/ruby/ruby/assets/31869/dc645cbe-9495-46f0-8485-24e790c42f32"> We're running far fewer OOBGC major GC's now that we have `GC.needs_major?` than we were before, and we believe that this is contributing to a slightly increased number of minor GC's. raising the p99 slightly. **App response times are all improved** We see a ~2% reduction in average response times when compared againststandard GC (~7% p99, ~3% p99.9 and ~4% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 17" src="https://gist.github.com/assets/31869/70e81fa5-77b2-469a-8945-88bf8f8fefe9"> This drops slightly to an a ~1% reduction in average response times when compared against our normal OOBGC approach (~6% p99, ~2% p99.9 and ~3% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 29" src="https://gist.github.com/assets/31869/cbaa3807-0cd1-4dba-a5e6-b9df91024d73"> EDIT: to correct a formula error in the original Average charts, numbers updated. ---Files-------------------------------- Capture d’écran 2024-04-22 à 18.41.52.png (279 KB) -- https://bugs.ruby-lang.org/

Issue #20443 has been updated by ko1 (Koichi Sasada). * `needs_major` "s" should not be on method name (like `File.exists` -> `File.exist`) * can you measure the memory consumption? It is a key compared with old OOBGC. ---------------------------------------- Feature #20443: Allow Major GC's to be disabled https://bugs.ruby-lang.org/issues/20443#change-108105 * Author: eightbitraptor (Matthew Valentine-House) * Status: Open ---------------------------------------- [[Github PR #10598]](https://github.com/ruby/ruby/pull/10598) ## Background Ruby's GC running during Rails requests can have negative impacts on currently running requests, causing applications to have high tail-latency. A technique to mitigate this high tail-latency is Out-of-band GC (OOBGC). This is basically where the application is run with GC disabled, and then GC is explicitly started after each request, or when no requests are in progress. This can reduce the tail latency, but also introduces problems of its own. Long GC pauses after each request reduce throughput. This is more pronounced on threading servers like Puma because all the threads have to finish processing user requests and be "paused" before OOBGC can be triggered. This throughput decrease happens for a couple of reasons: 1. There are few heuristics available for users to determine when GC should run, this means that in OOBGC scenarios, it's possible that major GC's are being run more than necessary. 2. The lack of any GC during a request means that lots of garbage objects have been created and not cleaned up, so the process is using more memory than it should - requiring major GC's run as part of OOBGC to do more work and therefore take more time. This ticket attempts to address these issues by: 1. Provide `GC.disable_major` and its antonym `GC.enable_major` to disable and enable only major GC 2. Provide `GC.needs_major?` as a basic heuristic allowing users to tell when Ruby should run a Major GC. These ideas were originally proposed by @ko1 and @byroot in [this rails issue](https://github.com/rails/rails/issues/50449) Disabling GC major's would still allow minor GC's to run during the request, avoiding the ballooning memory usage caused by not running GC at all, and reducing the time that a major takes when we do run it, because the nursery objects have been cleaned up during the request already so there is less work for a major GC to do. This can be used in combination with `GC.needs_major?` to selectively run an OOBGC only when necessary ## Implementation This PR adds 3 new methods to the `GC` module - `GC.disable_major` This prevents major GC's from running automatically. It does not restrict minors. When `objspace->rgengc.need_major_gc` is set and a GC is run, instead of running a major, new heap pages will be allocated and a minor run instead. `objspace->rgengc.need_major_gc` will remain set until a major is manually run. If a major is not manually run then the process will eventually run out of memory. When major GC's are disabled, object promotion is disabled. That is, no objects will increment their ages during a minor GC. This is to attempt to minimise heap growth during the period between major GC's, by restricting the number of old-gen objects that will remain unconsidered by the GC until the next major. When `GC.start` is run, then major GC's will be enabled, a GC triggered with the options passed to `GC.start`, and then `disable_major` will be set to the state it was in before `GC.start` was called. - `GC.enable_major` This simply unsets the bit preventing major GC's. This will revert the GC to normal generational behaviour. Everything behaves as default again. - `GC.needs_major?` This exposes the value of `objspace->rgengc.need_major_gc` to the user level API. This is already exposed in `GC.latest_gc_info[:need_major_by]` but I felt that a simpler interface would make this easier to use and result in more readable code. eg. ``` out_of_band do GC.start if GC.needs_major? end ``` Because object aging is disabled when majors are disabled it is recommended to use this in conjunction with `Process.warmup`, which will prepare the heap by running a major GC, compacting the heap, and promoting every remaining object to old-gen. This ensures that minor GC's are running over the smallets possible set of young objects when `GC.disable_major` is true. ## Benchmarks We ran some tests in production on Shopify's core monolith over a weekend and found that: **Mean time spent in GC, as well as p99.9 and p99.99 GC times are all improved.** <img width="1000" alt="Screenshot 2024-04-22 at 16 41 49" src="https://github.com/ruby/ruby/assets/31869/6cff5b11-2e21-40c1-bb84-d994e0e1798d"> **p99 GC time is slightly higher.** <img width="1000" alt="Screenshot 2024-04-22 at 16 44 55" src="https://github.com/ruby/ruby/assets/31869/dc645cbe-9495-46f0-8485-24e790c42f32"> We're running far fewer OOBGC major GC's now that we have `GC.needs_major?` than we were before, and we believe that this is contributing to a slightly increased number of minor GC's. raising the p99 slightly. **App response times are all improved** We see a ~2% reduction in average response times when compared againststandard GC (~7% p99, ~3% p99.9 and ~4% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 17" src="https://gist.github.com/assets/31869/70e81fa5-77b2-469a-8945-88bf8f8fefe9"> This drops slightly to an a ~1% reduction in average response times when compared against our normal OOBGC approach (~6% p99, ~2% p99.9 and ~3% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 29" src="https://gist.github.com/assets/31869/cbaa3807-0cd1-4dba-a5e6-b9df91024d73"> EDIT: to correct a formula error in the original Average charts, numbers updated. ---Files-------------------------------- Capture d’écran 2024-04-22 à 18.41.52.png (279 KB) -- https://bugs.ruby-lang.org/

Issue #20443 has been updated by byroot (Jean Boussier).

what happens on oldgen->younggen references? points from the remembers set?

Yes.

I think we can promote this case because it makes minor gc faster (the promoted objects can not be freed until major gc, so the number of living objects is same).

I understand your point, but I fear it could be counter-productive. We specifically stopped doing that in [Feature #19678] because there is many patterns in common Ruby code bases that are causing promotion. I'd rather run **minor GC** out of band frequently, and **major GC** out of band very rarely, because the ratio of effectively permanent objects to ephemeral ones tend to be large in long running applications. ---------------------------------------- Feature #20443: Allow Major GC's to be disabled https://bugs.ruby-lang.org/issues/20443#change-108110 * Author: eightbitraptor (Matthew Valentine-House) * Status: Open ---------------------------------------- [[Github PR #10598]](https://github.com/ruby/ruby/pull/10598) ## Background Ruby's GC running during Rails requests can have negative impacts on currently running requests, causing applications to have high tail-latency. A technique to mitigate this high tail-latency is Out-of-band GC (OOBGC). This is basically where the application is run with GC disabled, and then GC is explicitly started after each request, or when no requests are in progress. This can reduce the tail latency, but also introduces problems of its own. Long GC pauses after each request reduce throughput. This is more pronounced on threading servers like Puma because all the threads have to finish processing user requests and be "paused" before OOBGC can be triggered. This throughput decrease happens for a couple of reasons: 1. There are few heuristics available for users to determine when GC should run, this means that in OOBGC scenarios, it's possible that major GC's are being run more than necessary. 2. The lack of any GC during a request means that lots of garbage objects have been created and not cleaned up, so the process is using more memory than it should - requiring major GC's run as part of OOBGC to do more work and therefore take more time. This ticket attempts to address these issues by: 1. Provide `GC.disable_major` and its antonym `GC.enable_major` to disable and enable only major GC 2. Provide `GC.needs_major?` as a basic heuristic allowing users to tell when Ruby should run a Major GC. These ideas were originally proposed by @ko1 and @byroot in [this rails issue](https://github.com/rails/rails/issues/50449) Disabling GC major's would still allow minor GC's to run during the request, avoiding the ballooning memory usage caused by not running GC at all, and reducing the time that a major takes when we do run it, because the nursery objects have been cleaned up during the request already so there is less work for a major GC to do. This can be used in combination with `GC.needs_major?` to selectively run an OOBGC only when necessary ## Implementation This PR adds 3 new methods to the `GC` module - `GC.disable_major` This prevents major GC's from running automatically. It does not restrict minors. When `objspace->rgengc.need_major_gc` is set and a GC is run, instead of running a major, new heap pages will be allocated and a minor run instead. `objspace->rgengc.need_major_gc` will remain set until a major is manually run. If a major is not manually run then the process will eventually run out of memory. When major GC's are disabled, object promotion is disabled. That is, no objects will increment their ages during a minor GC. This is to attempt to minimise heap growth during the period between major GC's, by restricting the number of old-gen objects that will remain unconsidered by the GC until the next major. When `GC.start` is run, then major GC's will be enabled, a GC triggered with the options passed to `GC.start`, and then `disable_major` will be set to the state it was in before `GC.start` was called. - `GC.enable_major` This simply unsets the bit preventing major GC's. This will revert the GC to normal generational behaviour. Everything behaves as default again. - `GC.needs_major?` This exposes the value of `objspace->rgengc.need_major_gc` to the user level API. This is already exposed in `GC.latest_gc_info[:need_major_by]` but I felt that a simpler interface would make this easier to use and result in more readable code. eg. ``` out_of_band do GC.start if GC.needs_major? end ``` Because object aging is disabled when majors are disabled it is recommended to use this in conjunction with `Process.warmup`, which will prepare the heap by running a major GC, compacting the heap, and promoting every remaining object to old-gen. This ensures that minor GC's are running over the smallets possible set of young objects when `GC.disable_major` is true. ## Benchmarks We ran some tests in production on Shopify's core monolith over a weekend and found that: **Mean time spent in GC, as well as p99.9 and p99.99 GC times are all improved.** <img width="1000" alt="Screenshot 2024-04-22 at 16 41 49" src="https://github.com/ruby/ruby/assets/31869/6cff5b11-2e21-40c1-bb84-d994e0e1798d"> **p99 GC time is slightly higher.** <img width="1000" alt="Screenshot 2024-04-22 at 16 44 55" src="https://github.com/ruby/ruby/assets/31869/dc645cbe-9495-46f0-8485-24e790c42f32"> We're running far fewer OOBGC major GC's now that we have `GC.needs_major?` than we were before, and we believe that this is contributing to a slightly increased number of minor GC's. raising the p99 slightly. **App response times are all improved** We see a ~2% reduction in average response times when compared againststandard GC (~7% p99, ~3% p99.9 and ~4% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 17" src="https://gist.github.com/assets/31869/70e81fa5-77b2-469a-8945-88bf8f8fefe9"> This drops slightly to an a ~1% reduction in average response times when compared against our normal OOBGC approach (~6% p99, ~2% p99.9 and ~3% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 29" src="https://gist.github.com/assets/31869/cbaa3807-0cd1-4dba-a5e6-b9df91024d73"> EDIT: to correct a formula error in the original Average charts, numbers updated. ---Files-------------------------------- Capture d’écran 2024-04-22 à 18.41.52.png (279 KB) -- https://bugs.ruby-lang.org/

Issue #20443 has been updated by eightbitraptor (Matthew Valentine-House). matz (Yukihiro Matsumoto) wrote in #note-12:

I am neutral on this proposal. However, I am concerned that there may not be a Major GC when GC made pluggable.

Matz.

I think this is still relevant when GC is pluggable. Ruby will always ship with the existing GC by default, and there will always be applications for which running standard OOBGC will be the best approach. I would anticipate that this function would warn or become a no-op when a pluggable GC module is in use. ---------------------------------------- Feature #20443: Allow Major GC's to be disabled https://bugs.ruby-lang.org/issues/20443#change-108233 * Author: eightbitraptor (Matthew Valentine-House) * Status: Open ---------------------------------------- [[Github PR #10598]](https://github.com/ruby/ruby/pull/10598) ## Background Ruby's GC running during Rails requests can have negative impacts on currently running requests, causing applications to have high tail-latency. A technique to mitigate this high tail-latency is Out-of-band GC (OOBGC). This is basically where the application is run with GC disabled, and then GC is explicitly started after each request, or when no requests are in progress. This can reduce the tail latency, but also introduces problems of its own. Long GC pauses after each request reduce throughput. This is more pronounced on threading servers like Puma because all the threads have to finish processing user requests and be "paused" before OOBGC can be triggered. This throughput decrease happens for a couple of reasons: 1. There are few heuristics available for users to determine when GC should run, this means that in OOBGC scenarios, it's possible that major GC's are being run more than necessary. 2. The lack of any GC during a request means that lots of garbage objects have been created and not cleaned up, so the process is using more memory than it should - requiring major GC's run as part of OOBGC to do more work and therefore take more time. This ticket attempts to address these issues by: 1. Provide `GC.disable_major` and its antonym `GC.enable_major` to disable and enable only major GC 2. Provide `GC.needs_major?` as a basic heuristic allowing users to tell when Ruby should run a Major GC. These ideas were originally proposed by @ko1 and @byroot in [this rails issue](https://github.com/rails/rails/issues/50449) Disabling GC major's would still allow minor GC's to run during the request, avoiding the ballooning memory usage caused by not running GC at all, and reducing the time that a major takes when we do run it, because the nursery objects have been cleaned up during the request already so there is less work for a major GC to do. This can be used in combination with `GC.needs_major?` to selectively run an OOBGC only when necessary ## Implementation This PR adds 3 new methods to the `GC` module - `GC.disable_major` This prevents major GC's from running automatically. It does not restrict minors. When `objspace->rgengc.need_major_gc` is set and a GC is run, instead of running a major, new heap pages will be allocated and a minor run instead. `objspace->rgengc.need_major_gc` will remain set until a major is manually run. If a major is not manually run then the process will eventually run out of memory. When major GC's are disabled, object promotion is disabled. That is, no objects will increment their ages during a minor GC. This is to attempt to minimise heap growth during the period between major GC's, by restricting the number of old-gen objects that will remain unconsidered by the GC until the next major. When `GC.start` is run, then major GC's will be enabled, a GC triggered with the options passed to `GC.start`, and then `disable_major` will be set to the state it was in before `GC.start` was called. - `GC.enable_major` This simply unsets the bit preventing major GC's. This will revert the GC to normal generational behaviour. Everything behaves as default again. - `GC.needs_major?` This exposes the value of `objspace->rgengc.need_major_gc` to the user level API. This is already exposed in `GC.latest_gc_info[:need_major_by]` but I felt that a simpler interface would make this easier to use and result in more readable code. eg. ``` out_of_band do GC.start if GC.needs_major? end ``` Because object aging is disabled when majors are disabled it is recommended to use this in conjunction with `Process.warmup`, which will prepare the heap by running a major GC, compacting the heap, and promoting every remaining object to old-gen. This ensures that minor GC's are running over the smallets possible set of young objects when `GC.disable_major` is true. ## Benchmarks We ran some tests in production on Shopify's core monolith over a weekend and found that: **Mean time spent in GC, as well as p99.9 and p99.99 GC times are all improved.** <img width="1000" alt="Screenshot 2024-04-22 at 16 41 49" src="https://github.com/ruby/ruby/assets/31869/6cff5b11-2e21-40c1-bb84-d994e0e1798d"> **p99 GC time is slightly higher.** <img width="1000" alt="Screenshot 2024-04-22 at 16 44 55" src="https://github.com/ruby/ruby/assets/31869/dc645cbe-9495-46f0-8485-24e790c42f32"> We're running far fewer OOBGC major GC's now that we have `GC.needs_major?` than we were before, and we believe that this is contributing to a slightly increased number of minor GC's. raising the p99 slightly. **App response times are all improved** We see a ~2% reduction in average response times when compared againststandard GC (~7% p99, ~3% p99.9 and ~4% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 17" src="https://gist.github.com/assets/31869/70e81fa5-77b2-469a-8945-88bf8f8fefe9"> This drops slightly to an a ~1% reduction in average response times when compared against our normal OOBGC approach (~6% p99, ~2% p99.9 and ~3% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 29" src="https://gist.github.com/assets/31869/cbaa3807-0cd1-4dba-a5e6-b9df91024d73"> EDIT: to correct a formula error in the original Average charts, numbers updated. ---Files-------------------------------- Capture d’écran 2024-04-22 à 18.41.52.png (279 KB) -- https://bugs.ruby-lang.org/

Issue #20443 has been updated by matz (Yukihiro Matsumoto). As long as the pluggable GC issue is clearly stated somewhere, I have no objection. Matz. ---------------------------------------- Feature #20443: Allow Major GC's to be disabled https://bugs.ruby-lang.org/issues/20443#change-108283 * Author: eightbitraptor (Matthew Valentine-House) * Status: Open ---------------------------------------- [[Github PR #10598]](https://github.com/ruby/ruby/pull/10598) ## Background Ruby's GC running during Rails requests can have negative impacts on currently running requests, causing applications to have high tail-latency. A technique to mitigate this high tail-latency is Out-of-band GC (OOBGC). This is basically where the application is run with GC disabled, and then GC is explicitly started after each request, or when no requests are in progress. This can reduce the tail latency, but also introduces problems of its own. Long GC pauses after each request reduce throughput. This is more pronounced on threading servers like Puma because all the threads have to finish processing user requests and be "paused" before OOBGC can be triggered. This throughput decrease happens for a couple of reasons: 1. There are few heuristics available for users to determine when GC should run, this means that in OOBGC scenarios, it's possible that major GC's are being run more than necessary. 2. The lack of any GC during a request means that lots of garbage objects have been created and not cleaned up, so the process is using more memory than it should - requiring major GC's run as part of OOBGC to do more work and therefore take more time. This ticket attempts to address these issues by: 1. Provide `GC.disable_major` and its antonym `GC.enable_major` to disable and enable only major GC 2. Provide `GC.needs_major?` as a basic heuristic allowing users to tell when Ruby should run a Major GC. These ideas were originally proposed by @ko1 and @byroot in [this rails issue](https://github.com/rails/rails/issues/50449) Disabling GC major's would still allow minor GC's to run during the request, avoiding the ballooning memory usage caused by not running GC at all, and reducing the time that a major takes when we do run it, because the nursery objects have been cleaned up during the request already so there is less work for a major GC to do. This can be used in combination with `GC.needs_major?` to selectively run an OOBGC only when necessary ## Implementation This PR adds 3 new methods to the `GC` module - `GC.disable_major` This prevents major GC's from running automatically. It does not restrict minors. When `objspace->rgengc.need_major_gc` is set and a GC is run, instead of running a major, new heap pages will be allocated and a minor run instead. `objspace->rgengc.need_major_gc` will remain set until a major is manually run. If a major is not manually run then the process will eventually run out of memory. When major GC's are disabled, object promotion is disabled. That is, no objects will increment their ages during a minor GC. This is to attempt to minimise heap growth during the period between major GC's, by restricting the number of old-gen objects that will remain unconsidered by the GC until the next major. When `GC.start` is run, then major GC's will be enabled, a GC triggered with the options passed to `GC.start`, and then `disable_major` will be set to the state it was in before `GC.start` was called. - `GC.enable_major` This simply unsets the bit preventing major GC's. This will revert the GC to normal generational behaviour. Everything behaves as default again. - `GC.needs_major?` This exposes the value of `objspace->rgengc.need_major_gc` to the user level API. This is already exposed in `GC.latest_gc_info[:need_major_by]` but I felt that a simpler interface would make this easier to use and result in more readable code. eg. ``` out_of_band do GC.start if GC.needs_major? end ``` Because object aging is disabled when majors are disabled it is recommended to use this in conjunction with `Process.warmup`, which will prepare the heap by running a major GC, compacting the heap, and promoting every remaining object to old-gen. This ensures that minor GC's are running over the smallets possible set of young objects when `GC.disable_major` is true. ## Benchmarks We ran some tests in production on Shopify's core monolith over a weekend and found that: **Mean time spent in GC, as well as p99.9 and p99.99 GC times are all improved.** <img width="1000" alt="Screenshot 2024-04-22 at 16 41 49" src="https://github.com/ruby/ruby/assets/31869/6cff5b11-2e21-40c1-bb84-d994e0e1798d"> **p99 GC time is slightly higher.** <img width="1000" alt="Screenshot 2024-04-22 at 16 44 55" src="https://github.com/ruby/ruby/assets/31869/dc645cbe-9495-46f0-8485-24e790c42f32"> We're running far fewer OOBGC major GC's now that we have `GC.needs_major?` than we were before, and we believe that this is contributing to a slightly increased number of minor GC's. raising the p99 slightly. **App response times are all improved** We see a ~2% reduction in average response times when compared againststandard GC (~7% p99, ~3% p99.9 and ~4% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 17" src="https://gist.github.com/assets/31869/70e81fa5-77b2-469a-8945-88bf8f8fefe9"> This drops slightly to an a ~1% reduction in average response times when compared against our normal OOBGC approach (~6% p99, ~2% p99.9 and ~3% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 29" src="https://gist.github.com/assets/31869/cbaa3807-0cd1-4dba-a5e6-b9df91024d73"> EDIT: to correct a formula error in the original Average charts, numbers updated. ---Files-------------------------------- Capture d’écran 2024-04-22 à 18.41.52.png (279 KB) -- https://bugs.ruby-lang.org/

Issue #20443 has been updated by ko1 (Koichi Sasada). Proposed code just ignore `gc_aging` while "disable_major_gc" but it can increase aging up to 2 and next major gc makes the age 2 object to old object. In other words permanent objects can promote on single major gc easily. ---------------------------------------- Feature #20443: Allow Major GC's to be disabled https://bugs.ruby-lang.org/issues/20443#change-108595 * Author: eightbitraptor (Matthew Valentine-House) * Status: Open ---------------------------------------- [[Github PR #10598]](https://github.com/ruby/ruby/pull/10598) ## Background Ruby's GC running during Rails requests can have negative impacts on currently running requests, causing applications to have high tail-latency. A technique to mitigate this high tail-latency is Out-of-band GC (OOBGC). This is basically where the application is run with GC disabled, and then GC is explicitly started after each request, or when no requests are in progress. This can reduce the tail latency, but also introduces problems of its own. Long GC pauses after each request reduce throughput. This is more pronounced on threading servers like Puma because all the threads have to finish processing user requests and be "paused" before OOBGC can be triggered. This throughput decrease happens for a couple of reasons: 1. There are few heuristics available for users to determine when GC should run, this means that in OOBGC scenarios, it's possible that major GC's are being run more than necessary. 2. The lack of any GC during a request means that lots of garbage objects have been created and not cleaned up, so the process is using more memory than it should - requiring major GC's run as part of OOBGC to do more work and therefore take more time. This ticket attempts to address these issues by: 1. Provide `GC.disable_major` and its antonym `GC.enable_major` to disable and enable only major GC 2. Provide `GC.needs_major?` as a basic heuristic allowing users to tell when Ruby should run a Major GC. These ideas were originally proposed by @ko1 and @byroot in [this rails issue](https://github.com/rails/rails/issues/50449) Disabling GC major's would still allow minor GC's to run during the request, avoiding the ballooning memory usage caused by not running GC at all, and reducing the time that a major takes when we do run it, because the nursery objects have been cleaned up during the request already so there is less work for a major GC to do. This can be used in combination with `GC.needs_major?` to selectively run an OOBGC only when necessary ## Implementation This PR adds 3 new methods to the `GC` module - `GC.disable_major` This prevents major GC's from running automatically. It does not restrict minors. When `objspace->rgengc.need_major_gc` is set and a GC is run, instead of running a major, new heap pages will be allocated and a minor run instead. `objspace->rgengc.need_major_gc` will remain set until a major is manually run. If a major is not manually run then the process will eventually run out of memory. When major GC's are disabled, object promotion is disabled. That is, no objects will increment their ages during a minor GC. This is to attempt to minimise heap growth during the period between major GC's, by restricting the number of old-gen objects that will remain unconsidered by the GC until the next major. When `GC.start` is run, then major GC's will be enabled, a GC triggered with the options passed to `GC.start`, and then `disable_major` will be set to the state it was in before `GC.start` was called. - `GC.enable_major` This simply unsets the bit preventing major GC's. This will revert the GC to normal generational behaviour. Everything behaves as default again. - `GC.needs_major?` This exposes the value of `objspace->rgengc.need_major_gc` to the user level API. This is already exposed in `GC.latest_gc_info[:need_major_by]` but I felt that a simpler interface would make this easier to use and result in more readable code. eg. ``` out_of_band do GC.start if GC.needs_major? end ``` Because object aging is disabled when majors are disabled it is recommended to use this in conjunction with `Process.warmup`, which will prepare the heap by running a major GC, compacting the heap, and promoting every remaining object to old-gen. This ensures that minor GC's are running over the smallets possible set of young objects when `GC.disable_major` is true. ## Benchmarks We ran some tests in production on Shopify's core monolith over a weekend and found that: **Mean time spent in GC, as well as p99.9 and p99.99 GC times are all improved.** <img width="1000" alt="Screenshot 2024-04-22 at 16 41 49" src="https://github.com/ruby/ruby/assets/31869/6cff5b11-2e21-40c1-bb84-d994e0e1798d"> **p99 GC time is slightly higher.** <img width="1000" alt="Screenshot 2024-04-22 at 16 44 55" src="https://github.com/ruby/ruby/assets/31869/dc645cbe-9495-46f0-8485-24e790c42f32"> We're running far fewer OOBGC major GC's now that we have `GC.needs_major?` than we were before, and we believe that this is contributing to a slightly increased number of minor GC's. raising the p99 slightly. **App response times are all improved** We see a ~2% reduction in average response times when compared againststandard GC (~7% p99, ~3% p99.9 and ~4% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 17" src="https://gist.github.com/assets/31869/70e81fa5-77b2-469a-8945-88bf8f8fefe9"> This drops slightly to an a ~1% reduction in average response times when compared against our normal OOBGC approach (~6% p99, ~2% p99.9 and ~3% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 29" src="https://gist.github.com/assets/31869/cbaa3807-0cd1-4dba-a5e6-b9df91024d73"> EDIT: to correct a formula error in the original Average charts, numbers updated. ---Files-------------------------------- Capture d’écran 2024-04-22 à 18.41.52.png (279 KB) -- https://bugs.ruby-lang.org/

Issue #20443 has been updated by eightbitraptor (Matthew Valentine-House). eightbitraptor (Matthew Valentine-House) wrote in #note-18:

Thanks @ko1. I've updated the documentation as per @matz request, ~~so I'll merge and close this now.~~

I've discussed this further with @ko1 on Slack, who would like the names clarified at the next dev meeting. So this ticket will remain open for now. ---------------------------------------- Feature #20443: Allow Major GC's to be disabled https://bugs.ruby-lang.org/issues/20443#change-108608 * Author: eightbitraptor (Matthew Valentine-House) * Status: Open ---------------------------------------- [[Github PR #10598]](https://github.com/ruby/ruby/pull/10598) ## Background Ruby's GC running during Rails requests can have negative impacts on currently running requests, causing applications to have high tail-latency. A technique to mitigate this high tail-latency is Out-of-band GC (OOBGC). This is basically where the application is run with GC disabled, and then GC is explicitly started after each request, or when no requests are in progress. This can reduce the tail latency, but also introduces problems of its own. Long GC pauses after each request reduce throughput. This is more pronounced on threading servers like Puma because all the threads have to finish processing user requests and be "paused" before OOBGC can be triggered. This throughput decrease happens for a couple of reasons: 1. There are few heuristics available for users to determine when GC should run, this means that in OOBGC scenarios, it's possible that major GC's are being run more than necessary. 2. The lack of any GC during a request means that lots of garbage objects have been created and not cleaned up, so the process is using more memory than it should - requiring major GC's run as part of OOBGC to do more work and therefore take more time. This ticket attempts to address these issues by: 1. Provide `GC.disable_major` and its antonym `GC.enable_major` to disable and enable only major GC 2. Provide `GC.needs_major?` as a basic heuristic allowing users to tell when Ruby should run a Major GC. These ideas were originally proposed by @ko1 and @byroot in [this rails issue](https://github.com/rails/rails/issues/50449) Disabling GC major's would still allow minor GC's to run during the request, avoiding the ballooning memory usage caused by not running GC at all, and reducing the time that a major takes when we do run it, because the nursery objects have been cleaned up during the request already so there is less work for a major GC to do. This can be used in combination with `GC.needs_major?` to selectively run an OOBGC only when necessary ## Implementation This PR adds 3 new methods to the `GC` module - `GC.disable_major` This prevents major GC's from running automatically. It does not restrict minors. When `objspace->rgengc.need_major_gc` is set and a GC is run, instead of running a major, new heap pages will be allocated and a minor run instead. `objspace->rgengc.need_major_gc` will remain set until a major is manually run. If a major is not manually run then the process will eventually run out of memory. When major GC's are disabled, object promotion is disabled. That is, no objects will increment their ages during a minor GC. This is to attempt to minimise heap growth during the period between major GC's, by restricting the number of old-gen objects that will remain unconsidered by the GC until the next major. When `GC.start` is run, then major GC's will be enabled, a GC triggered with the options passed to `GC.start`, and then `disable_major` will be set to the state it was in before `GC.start` was called. - `GC.enable_major` This simply unsets the bit preventing major GC's. This will revert the GC to normal generational behaviour. Everything behaves as default again. - `GC.needs_major?` This exposes the value of `objspace->rgengc.need_major_gc` to the user level API. This is already exposed in `GC.latest_gc_info[:need_major_by]` but I felt that a simpler interface would make this easier to use and result in more readable code. eg. ``` out_of_band do GC.start if GC.needs_major? end ``` Because object aging is disabled when majors are disabled it is recommended to use this in conjunction with `Process.warmup`, which will prepare the heap by running a major GC, compacting the heap, and promoting every remaining object to old-gen. This ensures that minor GC's are running over the smallets possible set of young objects when `GC.disable_major` is true. ## Benchmarks We ran some tests in production on Shopify's core monolith over a weekend and found that: **Mean time spent in GC, as well as p99.9 and p99.99 GC times are all improved.** <img width="1000" alt="Screenshot 2024-04-22 at 16 41 49" src="https://github.com/ruby/ruby/assets/31869/6cff5b11-2e21-40c1-bb84-d994e0e1798d"> **p99 GC time is slightly higher.** <img width="1000" alt="Screenshot 2024-04-22 at 16 44 55" src="https://github.com/ruby/ruby/assets/31869/dc645cbe-9495-46f0-8485-24e790c42f32"> We're running far fewer OOBGC major GC's now that we have `GC.needs_major?` than we were before, and we believe that this is contributing to a slightly increased number of minor GC's. raising the p99 slightly. **App response times are all improved** We see a ~2% reduction in average response times when compared againststandard GC (~7% p99, ~3% p99.9 and ~4% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 17" src="https://gist.github.com/assets/31869/70e81fa5-77b2-469a-8945-88bf8f8fefe9"> This drops slightly to an a ~1% reduction in average response times when compared against our normal OOBGC approach (~6% p99, ~2% p99.9 and ~3% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 29" src="https://gist.github.com/assets/31869/cbaa3807-0cd1-4dba-a5e6-b9df91024d73"> EDIT: to correct a formula error in the original Average charts, numbers updated. ---Files-------------------------------- Capture d’écran 2024-04-22 à 18.41.52.png (279 KB) -- https://bugs.ruby-lang.org/

Issue #20443 has been updated by eightbitraptor (Matthew Valentine-House). matz (Yukihiro Matsumoto) wrote in #note-20:

First, If you clearly define what would happen when the (plugged) GC does not generational scanning, I am OK for it. @byroot told me that calling those methods would raise `NotImplementedError` when GC does not provide generational GC.

For API, I don't like the name `needs_major?`. At least, it should be `need_major?` to follow Ruby's naming convention (no third-person singular present).

And in the developers' meeting, @byroot proposed `GC.config(full_mark: true)`. How do you think?

Matz.

I really like the idea of having a set of config parameters to the GC. That seems like a much more robust way of providing custom features to the GC without having to make new methods every time. So, based on the latest discussions, what I'd like to propose is this: * Introduce `GC.config`, currently with a single key `full_mark`. * `full_mark: true` should be the default behaviour - ie. the GC will work as it currently does. * Ruby code can set `full_mark` to false like this: `GC.config(full_mark: false)` - In this case, no major GC's will be run unless explicitly requested using `GC.start(full_mark: true)` * A user can check whether a major GC is needed at any time by checking `GC.latest_gc_info(:needs_major_by)`. Any value other than `nil` means that the GC would do a major on the next invocation. I think this has a few benefits over the existing approach that I proposed in this ticket 1. Introduces a flexible way of providing config information to the GC. This will also allow pluggable GC's implemented in the future to define their own config keys without changing the interface of the `GC` module. 2. Does not introduce any new methods that are implementation specific to the current GC. This removes the decision about how future GC module needs to respond to these methods. ---------------------------------------- Feature #20443: Allow Major GC's to be disabled https://bugs.ruby-lang.org/issues/20443#change-108763 * Author: eightbitraptor (Matthew Valentine-House) * Status: Open ---------------------------------------- [[Github PR #10598]](https://github.com/ruby/ruby/pull/10598) ## Background Ruby's GC running during Rails requests can have negative impacts on currently running requests, causing applications to have high tail-latency. A technique to mitigate this high tail-latency is Out-of-band GC (OOBGC). This is basically where the application is run with GC disabled, and then GC is explicitly started after each request, or when no requests are in progress. This can reduce the tail latency, but also introduces problems of its own. Long GC pauses after each request reduce throughput. This is more pronounced on threading servers like Puma because all the threads have to finish processing user requests and be "paused" before OOBGC can be triggered. This throughput decrease happens for a couple of reasons: 1. There are few heuristics available for users to determine when GC should run, this means that in OOBGC scenarios, it's possible that major GC's are being run more than necessary. 2. The lack of any GC during a request means that lots of garbage objects have been created and not cleaned up, so the process is using more memory than it should - requiring major GC's run as part of OOBGC to do more work and therefore take more time. This ticket attempts to address these issues by: 1. Provide `GC.disable_major` and its antonym `GC.enable_major` to disable and enable only major GC 2. Provide `GC.needs_major?` as a basic heuristic allowing users to tell when Ruby should run a Major GC. These ideas were originally proposed by @ko1 and @byroot in [this rails issue](https://github.com/rails/rails/issues/50449) Disabling GC major's would still allow minor GC's to run during the request, avoiding the ballooning memory usage caused by not running GC at all, and reducing the time that a major takes when we do run it, because the nursery objects have been cleaned up during the request already so there is less work for a major GC to do. This can be used in combination with `GC.needs_major?` to selectively run an OOBGC only when necessary ## Implementation This PR adds 3 new methods to the `GC` module - `GC.disable_major` This prevents major GC's from running automatically. It does not restrict minors. When `objspace->rgengc.need_major_gc` is set and a GC is run, instead of running a major, new heap pages will be allocated and a minor run instead. `objspace->rgengc.need_major_gc` will remain set until a major is manually run. If a major is not manually run then the process will eventually run out of memory. When major GC's are disabled, object promotion is disabled. That is, no objects will increment their ages during a minor GC. This is to attempt to minimise heap growth during the period between major GC's, by restricting the number of old-gen objects that will remain unconsidered by the GC until the next major. When `GC.start` is run, then major GC's will be enabled, a GC triggered with the options passed to `GC.start`, and then `disable_major` will be set to the state it was in before `GC.start` was called. - `GC.enable_major` This simply unsets the bit preventing major GC's. This will revert the GC to normal generational behaviour. Everything behaves as default again. - `GC.needs_major?` This exposes the value of `objspace->rgengc.need_major_gc` to the user level API. This is already exposed in `GC.latest_gc_info[:need_major_by]` but I felt that a simpler interface would make this easier to use and result in more readable code. eg. ``` out_of_band do GC.start if GC.needs_major? end ``` Because object aging is disabled when majors are disabled it is recommended to use this in conjunction with `Process.warmup`, which will prepare the heap by running a major GC, compacting the heap, and promoting every remaining object to old-gen. This ensures that minor GC's are running over the smallets possible set of young objects when `GC.disable_major` is true. ## Benchmarks We ran some tests in production on Shopify's core monolith over a weekend and found that: **Mean time spent in GC, as well as p99.9 and p99.99 GC times are all improved.** <img width="1000" alt="Screenshot 2024-04-22 at 16 41 49" src="https://github.com/ruby/ruby/assets/31869/6cff5b11-2e21-40c1-bb84-d994e0e1798d"> **p99 GC time is slightly higher.** <img width="1000" alt="Screenshot 2024-04-22 at 16 44 55" src="https://github.com/ruby/ruby/assets/31869/dc645cbe-9495-46f0-8485-24e790c42f32"> We're running far fewer OOBGC major GC's now that we have `GC.needs_major?` than we were before, and we believe that this is contributing to a slightly increased number of minor GC's. raising the p99 slightly. **App response times are all improved** We see a ~2% reduction in average response times when compared againststandard GC (~7% p99, ~3% p99.9 and ~4% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 17" src="https://gist.github.com/assets/31869/70e81fa5-77b2-469a-8945-88bf8f8fefe9"> This drops slightly to an a ~1% reduction in average response times when compared against our normal OOBGC approach (~6% p99, ~2% p99.9 and ~3% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 29" src="https://gist.github.com/assets/31869/cbaa3807-0cd1-4dba-a5e6-b9df91024d73"> EDIT: to correct a formula error in the original Average charts, numbers updated. ---Files-------------------------------- Capture d’écran 2024-04-22 à 18.41.52.png (279 KB) -- https://bugs.ruby-lang.org/

Issue #20443 has been updated by byroot (Jean Boussier).

but not sure config or configure or other word? (English issue).

Given `GC.config` returns the current configuration, I can't be `.configure`. It could be `.configuration`, or any other concept. We can add it to the upcoming dev meeting to get a decision on that name. ---------------------------------------- Feature #20443: Allow Major GC's to be disabled https://bugs.ruby-lang.org/issues/20443#change-109011 * Author: eightbitraptor (Matthew Valentine-House) * Status: Open ---------------------------------------- [[Github PR #10598]](https://github.com/ruby/ruby/pull/10598) ## Background Ruby's GC running during Rails requests can have negative impacts on currently running requests, causing applications to have high tail-latency. A technique to mitigate this high tail-latency is Out-of-band GC (OOBGC). This is basically where the application is run with GC disabled, and then GC is explicitly started after each request, or when no requests are in progress. This can reduce the tail latency, but also introduces problems of its own. Long GC pauses after each request reduce throughput. This is more pronounced on threading servers like Puma because all the threads have to finish processing user requests and be "paused" before OOBGC can be triggered. This throughput decrease happens for a couple of reasons: 1. There are few heuristics available for users to determine when GC should run, this means that in OOBGC scenarios, it's possible that major GC's are being run more than necessary. 2. The lack of any GC during a request means that lots of garbage objects have been created and not cleaned up, so the process is using more memory than it should - requiring major GC's run as part of OOBGC to do more work and therefore take more time. This ticket attempts to address these issues by: 1. Provide `GC.disable_major` and its antonym `GC.enable_major` to disable and enable only major GC 2. Provide `GC.needs_major?` as a basic heuristic allowing users to tell when Ruby should run a Major GC. These ideas were originally proposed by @ko1 and @byroot in [this rails issue](https://github.com/rails/rails/issues/50449) Disabling GC major's would still allow minor GC's to run during the request, avoiding the ballooning memory usage caused by not running GC at all, and reducing the time that a major takes when we do run it, because the nursery objects have been cleaned up during the request already so there is less work for a major GC to do. This can be used in combination with `GC.needs_major?` to selectively run an OOBGC only when necessary ## Implementation This PR adds 3 new methods to the `GC` module - `GC.disable_major` This prevents major GC's from running automatically. It does not restrict minors. When `objspace->rgengc.need_major_gc` is set and a GC is run, instead of running a major, new heap pages will be allocated and a minor run instead. `objspace->rgengc.need_major_gc` will remain set until a major is manually run. If a major is not manually run then the process will eventually run out of memory. When major GC's are disabled, object promotion is disabled. That is, no objects will increment their ages during a minor GC. This is to attempt to minimise heap growth during the period between major GC's, by restricting the number of old-gen objects that will remain unconsidered by the GC until the next major. When `GC.start` is run, then major GC's will be enabled, a GC triggered with the options passed to `GC.start`, and then `disable_major` will be set to the state it was in before `GC.start` was called. - `GC.enable_major` This simply unsets the bit preventing major GC's. This will revert the GC to normal generational behaviour. Everything behaves as default again. - `GC.needs_major?` This exposes the value of `objspace->rgengc.need_major_gc` to the user level API. This is already exposed in `GC.latest_gc_info[:need_major_by]` but I felt that a simpler interface would make this easier to use and result in more readable code. eg. ``` out_of_band do GC.start if GC.needs_major? end ``` Because object aging is disabled when majors are disabled it is recommended to use this in conjunction with `Process.warmup`, which will prepare the heap by running a major GC, compacting the heap, and promoting every remaining object to old-gen. This ensures that minor GC's are running over the smallets possible set of young objects when `GC.disable_major` is true. ## Benchmarks We ran some tests in production on Shopify's core monolith over a weekend and found that: **Mean time spent in GC, as well as p99.9 and p99.99 GC times are all improved.** <img width="1000" alt="Screenshot 2024-04-22 at 16 41 49" src="https://github.com/ruby/ruby/assets/31869/6cff5b11-2e21-40c1-bb84-d994e0e1798d"> **p99 GC time is slightly higher.** <img width="1000" alt="Screenshot 2024-04-22 at 16 44 55" src="https://github.com/ruby/ruby/assets/31869/dc645cbe-9495-46f0-8485-24e790c42f32"> We're running far fewer OOBGC major GC's now that we have `GC.needs_major?` than we were before, and we believe that this is contributing to a slightly increased number of minor GC's. raising the p99 slightly. **App response times are all improved** We see a ~2% reduction in average response times when compared againststandard GC (~7% p99, ~3% p99.9 and ~4% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 17" src="https://gist.github.com/assets/31869/70e81fa5-77b2-469a-8945-88bf8f8fefe9"> This drops slightly to an a ~1% reduction in average response times when compared against our normal OOBGC approach (~6% p99, ~2% p99.9 and ~3% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 29" src="https://gist.github.com/assets/31869/cbaa3807-0cd1-4dba-a5e6-b9df91024d73"> EDIT: to correct a formula error in the original Average charts, numbers updated. ---Files-------------------------------- Capture d’écran 2024-04-22 à 18.41.52.png (279 KB) -- https://bugs.ruby-lang.org/

Issue #20443 has been updated by ko1 (Koichi Sasada). On dev-meeting, there is no objection on `GC.config()`. Could you write the more doc of it? For example, returning value is unclear. About keys: * Matz prefer to add prefix for the keys, like `GC.config(gengc_full_mark: true)`. * I think `GC.config(gengc_full_mark: true)` is not clear always do full marking or not (`gengc_full_mark: false` is clear that full marking is prohibited). `gengc_allow_full_mark: true/false`? too much? ---------------------------------------- Feature #20443: Allow Major GC's to be disabled https://bugs.ruby-lang.org/issues/20443#change-109080 * Author: eightbitraptor (Matthew Valentine-House) * Status: Open ---------------------------------------- [[Github PR #10598]](https://github.com/ruby/ruby/pull/10598) ## Background Ruby's GC running during Rails requests can have negative impacts on currently running requests, causing applications to have high tail-latency. A technique to mitigate this high tail-latency is Out-of-band GC (OOBGC). This is basically where the application is run with GC disabled, and then GC is explicitly started after each request, or when no requests are in progress. This can reduce the tail latency, but also introduces problems of its own. Long GC pauses after each request reduce throughput. This is more pronounced on threading servers like Puma because all the threads have to finish processing user requests and be "paused" before OOBGC can be triggered. This throughput decrease happens for a couple of reasons: 1. There are few heuristics available for users to determine when GC should run, this means that in OOBGC scenarios, it's possible that major GC's are being run more than necessary. 2. The lack of any GC during a request means that lots of garbage objects have been created and not cleaned up, so the process is using more memory than it should - requiring major GC's run as part of OOBGC to do more work and therefore take more time. This ticket attempts to address these issues by: 1. Provide `GC.disable_major` and its antonym `GC.enable_major` to disable and enable only major GC 2. Provide `GC.needs_major?` as a basic heuristic allowing users to tell when Ruby should run a Major GC. These ideas were originally proposed by @ko1 and @byroot in [this rails issue](https://github.com/rails/rails/issues/50449) Disabling GC major's would still allow minor GC's to run during the request, avoiding the ballooning memory usage caused by not running GC at all, and reducing the time that a major takes when we do run it, because the nursery objects have been cleaned up during the request already so there is less work for a major GC to do. This can be used in combination with `GC.needs_major?` to selectively run an OOBGC only when necessary ## Implementation This PR adds 3 new methods to the `GC` module - `GC.disable_major` This prevents major GC's from running automatically. It does not restrict minors. When `objspace->rgengc.need_major_gc` is set and a GC is run, instead of running a major, new heap pages will be allocated and a minor run instead. `objspace->rgengc.need_major_gc` will remain set until a major is manually run. If a major is not manually run then the process will eventually run out of memory. When major GC's are disabled, object promotion is disabled. That is, no objects will increment their ages during a minor GC. This is to attempt to minimise heap growth during the period between major GC's, by restricting the number of old-gen objects that will remain unconsidered by the GC until the next major. When `GC.start` is run, then major GC's will be enabled, a GC triggered with the options passed to `GC.start`, and then `disable_major` will be set to the state it was in before `GC.start` was called. - `GC.enable_major` This simply unsets the bit preventing major GC's. This will revert the GC to normal generational behaviour. Everything behaves as default again. - `GC.needs_major?` This exposes the value of `objspace->rgengc.need_major_gc` to the user level API. This is already exposed in `GC.latest_gc_info[:need_major_by]` but I felt that a simpler interface would make this easier to use and result in more readable code. eg. ``` out_of_band do GC.start if GC.needs_major? end ``` Because object aging is disabled when majors are disabled it is recommended to use this in conjunction with `Process.warmup`, which will prepare the heap by running a major GC, compacting the heap, and promoting every remaining object to old-gen. This ensures that minor GC's are running over the smallets possible set of young objects when `GC.disable_major` is true. ## Benchmarks We ran some tests in production on Shopify's core monolith over a weekend and found that: **Mean time spent in GC, as well as p99.9 and p99.99 GC times are all improved.** <img width="1000" alt="Screenshot 2024-04-22 at 16 41 49" src="https://github.com/ruby/ruby/assets/31869/6cff5b11-2e21-40c1-bb84-d994e0e1798d"> **p99 GC time is slightly higher.** <img width="1000" alt="Screenshot 2024-04-22 at 16 44 55" src="https://github.com/ruby/ruby/assets/31869/dc645cbe-9495-46f0-8485-24e790c42f32"> We're running far fewer OOBGC major GC's now that we have `GC.needs_major?` than we were before, and we believe that this is contributing to a slightly increased number of minor GC's. raising the p99 slightly. **App response times are all improved** We see a ~2% reduction in average response times when compared againststandard GC (~7% p99, ~3% p99.9 and ~4% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 17" src="https://gist.github.com/assets/31869/70e81fa5-77b2-469a-8945-88bf8f8fefe9"> This drops slightly to an a ~1% reduction in average response times when compared against our normal OOBGC approach (~6% p99, ~2% p99.9 and ~3% p99.99). <img width="1000" alt="Screenshot 2024-04-23 at 09 27 29" src="https://gist.github.com/assets/31869/cbaa3807-0cd1-4dba-a5e6-b9df91024d73"> EDIT: to correct a formula error in the original Average charts, numbers updated. ---Files-------------------------------- Capture d’écran 2024-04-22 à 18.41.52.png (279 KB) -- https://bugs.ruby-lang.org/