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[5.15] Add memcg regression patch for 5.15-rc
See here for more info: https://www.phoronix.com/scan.php?page=article&item=linux515-performance-fix&num=1 To start compiling: 5.15-rc2: KERNEL_SRC_URI="https://git.kernel.org/torvalds/t" KERNEL_SRC_EXT="tar.gz" KERNEL_BASE_VER=5.15 KERNEL_PATCH_VER=5.15-rc2 KERNEL_SUB_VER=051500rc2 ./build_kernel.sh 5.15-rc2-rt3 (real-time kernel): KERNEL_TYPE=rt KERNEL_SRC_URI="https://git.kernel.org/torvalds/t" KERNEL_SRC_EXT="tar.gz" KERNEL_SCHEDULER=cfs KERNEL_BASE_VER=5.15 KERNEL_PATCH_VER=5.15-rc2 KERNEL_SUB_VER=051500rc2 ./build_kernel.sh Optional variables that may also be applicable for you: AMDGPU_BUILTIN=yes (for AMD graphic cards) VBOX_SUPPORT=yes (for VIrtualBox support)
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* [PATCH] memcg: flush lruvec stats in the refault | ||
@ 2021-09-22 22:49 Shakeel Butt | ||
2021-09-23 10:02 ` Michael Larabel | ||
0 siblings, 1 reply; 2+ messages in thread | ||
From: Shakeel Butt @ 2021-09-22 22:49 UTC (permalink / raw) | ||
To: Johannes Weiner | ||
Cc: Roman Gushchin, Michael Larabel, Feng Tang, Michal Hocko, | ||
Hillf Danton, Michal Koutný, | ||
Andrew Morton, Linus Torvalds, cgroups, linux-mm, linux-kernel, | ||
Shakeel Butt | ||
|
||
Prior to the commit 7e1c0d6f5820 ("memcg: switch lruvec stats to rstat") | ||
and the commit aa48e47e3906 ("memcg: infrastructure to flush memcg | ||
stats"), each lruvec memcg stats can be off by (nr_cgroups * nr_cpus * | ||
32) at worst and for unbounded amount of time. The commit aa48e47e3906 | ||
moved the lruvec stats to rstat infrastructure and the commit | ||
7e1c0d6f5820 bounded the error for all the lruvec stats to (nr_cpus * | ||
32) at worst for at most 2 seconds. More specifically it decoupled the | ||
number of stats and the number of cgroups from the error rate. | ||
|
||
However this reduction in error comes with the cost of triggering the | ||
slowpath of stats update more frequently. Previously in the slowpath the | ||
kernel adds the stats up the memcg tree. After aa48e47e3906, the kernel | ||
triggers the asyn lruvec stats flush through queue_work(). This causes | ||
regression reports from 0day kernel bot [1] as well as from phoronix | ||
test suite [2]. | ||
|
||
We tried two options to fix the regression: | ||
|
||
1) Increase the threshold to trigger the slowpath in lruvec stats update | ||
codepath from 32 to 512. | ||
|
||
2) Remove the slowpath from lruvec stats update codepath and instead | ||
flush the stats in the page refault codepath. The assumption is that the | ||
kernel timely flush the stats, so, the update tree would be small in the | ||
refault codepath to not cause the preformance impact. | ||
|
||
Following are the results of will-it-scale/page_fault[1|2|3] benchmark | ||
on four settings i.e. (1) 5.15-rc1 as baseline (2) 5.15-rc1 with | ||
aa48e47e3906 and 7e1c0d6f5820 reverted (3) 5.15-rc1 with option-1 | ||
(4) 5.15-rc1 with option-2. | ||
|
||
test (1) (2) (3) (4) | ||
pg_f1 368563 406277 (10.23%) 399693 (8.44%) 416398 (12.97%) | ||
pg_f2 338399 372133 (9.96%) 369180 (9.09%) 381024 (12.59%) | ||
pg_f3 500853 575399 (14.88%) 570388 (13.88%) 576083 (15.02%) | ||
|
||
From the above result, it seems like the option-2 not only solves the | ||
regression but also improves the performance for at least these | ||
benchmarks. | ||
|
||
Feng Tang (intel) ran the aim7 benchmark with these two options and | ||
confirms that option-1 reduces the regression but option-2 removes the | ||
regression. | ||
|
||
Michael Larabel (phoronix) ran multiple benchmarks with these options | ||
and reported the results at [3] and it shows for most benchmarks | ||
option-2 removes the regression introduced by the commit aa48e47e3906 | ||
("memcg: infrastructure to flush memcg stats"). | ||
|
||
Based on the experiment results, this patch proposed the option-2 as the | ||
solution to resolve the regression. | ||
|
||
[1] https://lore.kernel.org/all/20210726022421.GB21872@xsang-OptiPlex-9020 | ||
[2] https://www.phoronix.com/scan.php?page=article&item=linux515-compile-regress | ||
[3] https://openbenchmarking.org/result/2109226-DEBU-LINUX5104 | ||
|
||
Fixes: aa48e47e3906 ("memcg: infrastructure to flush memcg stats") | ||
Signed-off-by: Shakeel Butt <shakeelb@google.com> | ||
--- | ||
mm/memcontrol.c | 10 ---------- | ||
mm/workingset.c | 1 + | ||
2 files changed, 1 insertion(+), 10 deletions(-) | ||
|
||
diff --git a/mm/memcontrol.c b/mm/memcontrol.c | ||
index b762215d73eb..6da5020a8656 100644 | ||
--- a/mm/memcontrol.c | ||
+++ b/mm/memcontrol.c | ||
@@ -106,9 +106,6 @@ static bool do_memsw_account(void) | ||
/* memcg and lruvec stats flushing */ | ||
static void flush_memcg_stats_dwork(struct work_struct *w); | ||
static DECLARE_DEFERRABLE_WORK(stats_flush_dwork, flush_memcg_stats_dwork); | ||
-static void flush_memcg_stats_work(struct work_struct *w); | ||
-static DECLARE_WORK(stats_flush_work, flush_memcg_stats_work); | ||
-static DEFINE_PER_CPU(unsigned int, stats_flush_threshold); | ||
static DEFINE_SPINLOCK(stats_flush_lock); | ||
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||
#define THRESHOLDS_EVENTS_TARGET 128 | ||
@@ -682,8 +679,6 @@ void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx, | ||
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||
/* Update lruvec */ | ||
__this_cpu_add(pn->lruvec_stats_percpu->state[idx], val); | ||
- if (!(__this_cpu_inc_return(stats_flush_threshold) % MEMCG_CHARGE_BATCH)) | ||
- queue_work(system_unbound_wq, &stats_flush_work); | ||
} | ||
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||
/** | ||
@@ -5361,11 +5356,6 @@ static void flush_memcg_stats_dwork(struct work_struct *w) | ||
queue_delayed_work(system_unbound_wq, &stats_flush_dwork, 2UL*HZ); | ||
} | ||
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||
-static void flush_memcg_stats_work(struct work_struct *w) | ||
-{ | ||
- mem_cgroup_flush_stats(); | ||
-} | ||
- | ||
static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu) | ||
{ | ||
struct mem_cgroup *memcg = mem_cgroup_from_css(css); | ||
diff --git a/mm/workingset.c b/mm/workingset.c | ||
index d4268d8e9a82..d5b81e4f4cbe 100644 | ||
--- a/mm/workingset.c | ||
+++ b/mm/workingset.c | ||
@@ -352,6 +352,7 @@ void workingset_refault(struct page *page, void *shadow) | ||
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inc_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file); | ||
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+ mem_cgroup_flush_stats(); | ||
/* | ||
* Compare the distance to the existing workingset size. We | ||
* don't activate pages that couldn't stay resident even if | ||
-- | ||
2.33.0.464.g1972c5931b-goog | ||
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||
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^ permalink raw reply [flat|nested] 2+ messages in thread | ||
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* Re: [PATCH] memcg: flush lruvec stats in the refault | ||
2021-09-22 22:49 [PATCH] memcg: flush lruvec stats in the refault Shakeel Butt | ||
@ 2021-09-23 10:02 ` Michael Larabel | ||
0 siblings, 0 replies; 2+ messages in thread | ||
From: Michael Larabel @ 2021-09-23 10:02 UTC (permalink / raw) | ||
To: Shakeel Butt, Johannes Weiner | ||
Cc: Roman Gushchin, Feng Tang, Michal Hocko, Hillf Danton, | ||
Michal Koutný, | ||
Andrew Morton, Linus Torvalds, cgroups, linux-mm, linux-kernel | ||
|
||
On 9/22/21 5:49 PM, Shakeel Butt wrote: | ||
> Prior to the commit 7e1c0d6f5820 ("memcg: switch lruvec stats to rstat") | ||
> and the commit aa48e47e3906 ("memcg: infrastructure to flush memcg | ||
> stats"), each lruvec memcg stats can be off by (nr_cgroups * nr_cpus * | ||
> 32) at worst and for unbounded amount of time. The commit aa48e47e3906 | ||
> moved the lruvec stats to rstat infrastructure and the commit | ||
> 7e1c0d6f5820 bounded the error for all the lruvec stats to (nr_cpus * | ||
> 32) at worst for at most 2 seconds. More specifically it decoupled the | ||
> number of stats and the number of cgroups from the error rate. | ||
> | ||
> However this reduction in error comes with the cost of triggering the | ||
> slowpath of stats update more frequently. Previously in the slowpath the | ||
> kernel adds the stats up the memcg tree. After aa48e47e3906, the kernel | ||
> triggers the asyn lruvec stats flush through queue_work(). This causes | ||
> regression reports from 0day kernel bot [1] as well as from phoronix | ||
> test suite [2]. | ||
> | ||
> We tried two options to fix the regression: | ||
> | ||
> 1) Increase the threshold to trigger the slowpath in lruvec stats update | ||
> codepath from 32 to 512. | ||
> | ||
> 2) Remove the slowpath from lruvec stats update codepath and instead | ||
> flush the stats in the page refault codepath. The assumption is that the | ||
> kernel timely flush the stats, so, the update tree would be small in the | ||
> refault codepath to not cause the preformance impact. | ||
> | ||
> Following are the results of will-it-scale/page_fault[1|2|3] benchmark | ||
> on four settings i.e. (1) 5.15-rc1 as baseline (2) 5.15-rc1 with | ||
> aa48e47e3906 and 7e1c0d6f5820 reverted (3) 5.15-rc1 with option-1 | ||
> (4) 5.15-rc1 with option-2. | ||
> | ||
> test (1) (2) (3) (4) | ||
> pg_f1 368563 406277 (10.23%) 399693 (8.44%) 416398 (12.97%) | ||
> pg_f2 338399 372133 (9.96%) 369180 (9.09%) 381024 (12.59%) | ||
> pg_f3 500853 575399 (14.88%) 570388 (13.88%) 576083 (15.02%) | ||
> | ||
> From the above result, it seems like the option-2 not only solves the | ||
> regression but also improves the performance for at least these | ||
> benchmarks. | ||
> | ||
> Feng Tang (intel) ran the aim7 benchmark with these two options and | ||
> confirms that option-1 reduces the regression but option-2 removes the | ||
> regression. | ||
> | ||
> Michael Larabel (phoronix) ran multiple benchmarks with these options | ||
> and reported the results at [3] and it shows for most benchmarks | ||
> option-2 removes the regression introduced by the commit aa48e47e3906 | ||
> ("memcg: infrastructure to flush memcg stats"). | ||
> | ||
> Based on the experiment results, this patch proposed the option-2 as the | ||
> solution to resolve the regression. | ||
> | ||
> [1] https://lore.kernel.org/all/20210726022421.GB21872@xsang-OptiPlex-9020 | ||
> [2] https://www.phoronix.com/scan.php?page=article&item=linux515-compile-regress | ||
> [3] https://openbenchmarking.org/result/2109226-DEBU-LINUX5104 | ||
> | ||
> Fixes: aa48e47e3906 ("memcg: infrastructure to flush memcg stats") | ||
> Signed-off-by: Shakeel Butt <shakeelb@google.com> | ||
> --- | ||
> mm/memcontrol.c | 10 ---------- | ||
> mm/workingset.c | 1 + | ||
> 2 files changed, 1 insertion(+), 10 deletions(-) | ||
> | ||
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c | ||
> index b762215d73eb..6da5020a8656 100644 | ||
> --- a/mm/memcontrol.c | ||
> +++ b/mm/memcontrol.c | ||
> @@ -106,9 +106,6 @@ static bool do_memsw_account(void) | ||
> /* memcg and lruvec stats flushing */ | ||
> static void flush_memcg_stats_dwork(struct work_struct *w); | ||
> static DECLARE_DEFERRABLE_WORK(stats_flush_dwork, flush_memcg_stats_dwork); | ||
> -static void flush_memcg_stats_work(struct work_struct *w); | ||
> -static DECLARE_WORK(stats_flush_work, flush_memcg_stats_work); | ||
> -static DEFINE_PER_CPU(unsigned int, stats_flush_threshold); | ||
> static DEFINE_SPINLOCK(stats_flush_lock); | ||
> | ||
> #define THRESHOLDS_EVENTS_TARGET 128 | ||
> @@ -682,8 +679,6 @@ void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx, | ||
> | ||
> /* Update lruvec */ | ||
> __this_cpu_add(pn->lruvec_stats_percpu->state[idx], val); | ||
> - if (!(__this_cpu_inc_return(stats_flush_threshold) % MEMCG_CHARGE_BATCH)) | ||
> - queue_work(system_unbound_wq, &stats_flush_work); | ||
> } | ||
> | ||
> /** | ||
> @@ -5361,11 +5356,6 @@ static void flush_memcg_stats_dwork(struct work_struct *w) | ||
> queue_delayed_work(system_unbound_wq, &stats_flush_dwork, 2UL*HZ); | ||
> } | ||
> | ||
> -static void flush_memcg_stats_work(struct work_struct *w) | ||
> -{ | ||
> - mem_cgroup_flush_stats(); | ||
> -} | ||
> - | ||
> static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu) | ||
> { | ||
> struct mem_cgroup *memcg = mem_cgroup_from_css(css); | ||
> diff --git a/mm/workingset.c b/mm/workingset.c | ||
> index d4268d8e9a82..d5b81e4f4cbe 100644 | ||
> --- a/mm/workingset.c | ||
> +++ b/mm/workingset.c | ||
> @@ -352,6 +352,7 @@ void workingset_refault(struct page *page, void *shadow) | ||
> | ||
> inc_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file); | ||
> | ||
> + mem_cgroup_flush_stats(); | ||
> /* | ||
> * Compare the distance to the existing workingset size. We | ||
> * don't activate pages that couldn't stay resident even if | ||
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This patch is still looking good in my additional testing so far. | ||
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With an Intel Core i9 11900K system where it was quite noticeably | ||
regressing in various workloads, things now seem to be under control[1] | ||
with this patch and inline with v5.14 / 5.15 with the memcg patches | ||
reverted. | ||
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If desired: | ||
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Tested-by: Michael Larabel <Michael@phoronix.com> | ||
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Michael | ||
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[1] | ||
https://openbenchmarking.org/result/2109221-DEBU-LINUX5143&sgm=1&hgv=flush-in-the-ref&sor |