* [linux-next:master] [mm/vmpressure] ea928e9e18: stress-ng.mremap.ops_per_sec 36.2% regression
@ 2026-08-13 13:16 kernel test robot
2026-08-13 17:01 ` Shakeel Butt
0 siblings, 1 reply; 4+ messages in thread
From: kernel test robot @ 2026-08-13 13:16 UTC (permalink / raw)
To: Usama Arif
Cc: oe-lkp, lkp, Andrew Morton, Shakeel Butt, David Hildenbrand,
Johannes Weiner, Liam R. Howlett, Lorenzo Stoakes, Michal Hocko,
Michal Koutný, Mike Rapoport, Roman Gushchin,
Suren Baghdasaryan, Tejun Heo, Vlastimil Babka, linux-mm, cgroups,
yi1.lai
Hello,
kernel test robot noticed a 36.2% regression of stress-ng.mremap.ops_per_sec on:
commit: ea928e9e18da682e9a5bc40aa862bff7ce5ae42e ("mm/vmpressure: move v1 userspace eventfd code into memcontrol-v1.c") https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
in testcase: stress-ng
version: stress-ng-x86_64-29ce10a2c-1_20260712
with following parameters:
nr_threads: 100%
testtime: 60s
test: mremap
cpufreq_governor: performance
config: x86_64-rhel-9.4 (CONFIG_MEMCG=y and CONFIG_MEMCG_V1 is not set)
compiler: gcc-14
test machine: 256 threads 4 sockets INTEL(R) XEON(R) PLATINUM 8592+ (Emerald Rapids) with 256G memory
(please refer to attached dmesg/kmsg for entire log/backtrace)
If you fix the issue in a separate patch/commit (i.e. not just a new version of the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <yi1.lai@intel.com>
| Closes: https://lore.kernel.org/oe-lkp/202608131743.c6a7dda4-lkp@intel.com
2026-08-11 09:13:23 sysctl -w kernel.sched_autogroup_enabled=0 kernel.sched_autogroup_enabled = 0
2026-08-11 09:13:23 stress-ng --timeout 60 --times --verify --metrics --no-rand-seed --mremap 256
stress-ng: info: [10886] setting to a 1 min run per stressor
stress-ng: info: [10886] dispatching hogs: 256 mremap
stress-ng: info: [11033] mremap: using 1MB per stressor instance (total 256MB of 243.06GB available memory)
stress-ng: metrc: [10886] stressor bogo ops real time usr time sys time bogo ops/s bogo ops/s CPU used per RSS Max
stress-ng: metrc: [10886] (secs) (secs) (secs) (real time) (usr+sys time) instance (%) (KB)
stress-ng: metrc: [10886] mremap 2212529 59.96 209.34 15014.92 36901.22 145.33 99.19 6684
stress-ng: metrc: [10886] miscellaneous metrics:
stress-ng: metrc: [10886] mremap 151372.07 nanosecs per mremap call (harmonic mean of 256 instances)
stress-ng: info: [10886] for a 60.01s run time:
stress-ng: info: [10886] 15363.58s available CPU time
stress-ng: info: [10886] 209.34s user time ( 1.36%)
stress-ng: info: [10886] 15015.19s system time ( 97.73%)
stress-ng: info: [10886] 15224.53s total time ( 99.09%)
stress-ng: info: [10886] load average: 163.54 47.28 16.30
stress-ng: info: [10886] skipped: 0
stress-ng: info: [10886] passed: 256: mremap (256)
stress-ng: info: [10886] failed: 0
stress-ng: info: [10886] metrics untrustworthy: 0
stress-ng: info: [10886] successful run completed in 1 min
The kernel config and materials to reproduce are available at:
https://download.01.org/0day-ci/archive/20260813/202608131743.c6a7dda4-lkp@intel.com
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [linux-next:master] [mm/vmpressure] ea928e9e18: stress-ng.mremap.ops_per_sec 36.2% regression 2026-08-13 13:16 [linux-next:master] [mm/vmpressure] ea928e9e18: stress-ng.mremap.ops_per_sec 36.2% regression kernel test robot @ 2026-08-13 17:01 ` Shakeel Butt 2026-08-13 17:14 ` Usama Arif 0 siblings, 1 reply; 4+ messages in thread From: Shakeel Butt @ 2026-08-13 17:01 UTC (permalink / raw) To: kernel test robot Cc: Usama Arif, oe-lkp, lkp, Andrew Morton, David Hildenbrand, Johannes Weiner, Liam R. Howlett, Lorenzo Stoakes, Michal Hocko, Michal Koutný, Mike Rapoport, Roman Gushchin, Suren Baghdasaryan, Tejun Heo, Vlastimil Babka, linux-mm, cgroups On Thu, Aug 13, 2026 at 09:16:22PM +0800, kernel test robot wrote: > > > Hello, > > kernel test robot noticed a 36.2% regression of stress-ng.mremap.ops_per_sec on: > > commit: ea928e9e18da682e9a5bc40aa862bff7ce5ae42e ("mm/vmpressure: move v1 userspace eventfd code into memcontrol-v1.c") https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master > > in testcase: stress-ng > version: stress-ng-x86_64-29ce10a2c-1_20260712 > with following parameters: > > nr_threads: 100% > testtime: 60s > test: mremap > cpufreq_governor: performance > > > > config: x86_64-rhel-9.4 (CONFIG_MEMCG=y and CONFIG_MEMCG_V1 is not set) > compiler: gcc-14 > test machine: 256 threads 4 sockets INTEL(R) XEON(R) PLATINUM 8592+ (Emerald Rapids) with 256G memory > > (please refer to attached dmesg/kmsg for entire log/backtrace) > Hi there, Can you please test the following patch and see if it fixes the regression? From 84c0b05b3bc5cf73ee66ead75aafb1ad684462c3 Mon Sep 17 00:00:00 2001 From: Shakeel Butt <shakeel.butt@linux.dev> Date: Thu, 13 Aug 2026 09:38:28 -0700 Subject: [PATCH] memcg: keep vmstats_percpu off the memory_events[] cacheline Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev> --- include/linux/memcontrol.h | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index e78bc98ab229..e25d5b9a1db8 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -246,8 +246,13 @@ struct mem_cgroup { /* handle for "memory.swap.events" */ struct cgroup_file swap_events_file; - /* memory.stat */ + /* Read-mostly. */ struct memcg_vmstats *vmstats; + struct memcg_vmstats_percpu __percpu *vmstats_percpu; + int kmemcg_id; + + /* Write-hot from here on; do not let it share with the above. */ + CACHELINE_PADDING(_pad_); /* memory.events */ atomic_long_t memory_events[MEMCG_NR_MEMORY_EVENTS]; @@ -266,9 +271,6 @@ struct mem_cgroup { #if BITS_PER_LONG < 64 seqlock_t socket_pressure_seqlock; #endif - int kmemcg_id; - - struct memcg_vmstats_percpu __percpu *vmstats_percpu; #ifdef CONFIG_CGROUP_WRITEBACK struct list_head cgwb_list; -- 2.53.0-Meta ^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [linux-next:master] [mm/vmpressure] ea928e9e18: stress-ng.mremap.ops_per_sec 36.2% regression 2026-08-13 17:01 ` Shakeel Butt @ 2026-08-13 17:14 ` Usama Arif [not found] ` <an3-aksL0MZPM3ZJ@linux.dev> 0 siblings, 1 reply; 4+ messages in thread From: Usama Arif @ 2026-08-13 17:14 UTC (permalink / raw) To: Shakeel Butt, kernel test robot Cc: oe-lkp, lkp, Andrew Morton, David Hildenbrand, Johannes Weiner, Liam R. Howlett, Lorenzo Stoakes, Michal Hocko, Michal Koutný, Mike Rapoport, Roman Gushchin, Suren Baghdasaryan, Tejun Heo, Vlastimil Babka, linux-mm, cgroups On 13/08/2026 18:01, Shakeel Butt wrote: > On Thu, Aug 13, 2026 at 09:16:22PM +0800, kernel test robot wrote: >> >> >> Hello, >> >> kernel test robot noticed a 36.2% regression of stress-ng.mremap.ops_per_sec on: >> >> commit: ea928e9e18da682e9a5bc40aa862bff7ce5ae42e ("mm/vmpressure: move v1 userspace eventfd code into memcontrol-v1.c") https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master >> >> in testcase: stress-ng >> version: stress-ng-x86_64-29ce10a2c-1_20260712 >> with following parameters: >> >> nr_threads: 100% >> testtime: 60s >> test: mremap >> cpufreq_governor: performance >> >> >> >> config: x86_64-rhel-9.4 (CONFIG_MEMCG=y and CONFIG_MEMCG_V1 is not set) >> compiler: gcc-14 >> test machine: 256 threads 4 sockets INTEL(R) XEON(R) PLATINUM 8592+ (Emerald Rapids) with 256G memory >> >> (please refer to attached dmesg/kmsg for entire log/backtrace) >> > > Hi there, > > Can you please test the following patch and see if it fixes the regression? > > > From 84c0b05b3bc5cf73ee66ead75aafb1ad684462c3 Mon Sep 17 00:00:00 2001 > From: Shakeel Butt <shakeel.butt@linux.dev> > Date: Thu, 13 Aug 2026 09:38:28 -0700 > Subject: [PATCH] memcg: keep vmstats_percpu off the memory_events[] cacheline > > Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev> > --- > include/linux/memcontrol.h | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index e78bc98ab229..e25d5b9a1db8 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -246,8 +246,13 @@ struct mem_cgroup { > /* handle for "memory.swap.events" */ > struct cgroup_file swap_events_file; > > - /* memory.stat */ > + /* Read-mostly. */ > struct memcg_vmstats *vmstats; > + struct memcg_vmstats_percpu __percpu *vmstats_percpu; > + int kmemcg_id; > + > + /* Write-hot from here on; do not let it share with the above. */ > + CACHELINE_PADDING(_pad_); > > /* memory.events */ > atomic_long_t memory_events[MEMCG_NR_MEMORY_EVENTS]; > @@ -266,9 +271,6 @@ struct mem_cgroup { > #if BITS_PER_LONG < 64 > seqlock_t socket_pressure_seqlock; > #endif > - int kmemcg_id; > - > - struct memcg_vmstats_percpu __percpu *vmstats_percpu; > > #ifdef CONFIG_CGROUP_WRITEBACK > struct list_head cgwb_list; I was currently testing this diff, not sure which one would be better. diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index e78bc98ab229b..215e2e87f42b2 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -268,10 +268,15 @@ struct mem_cgroup { #endif int kmemcg_id; - struct memcg_vmstats_percpu __percpu *vmstats_percpu; - #ifdef CONFIG_CGROUP_WRITEBACK struct list_head cgwb_list; +#endif + + /* Keep the hot per-CPU stats pointer away from memory event counters. */ + struct memcg_vmstats_percpu __percpu *vmstats_percpu + ____cacheline_aligned_in_smp; + +#ifdef CONFIG_CGROUP_WRITEBACK struct wb_domain cgwb_domain; struct memcg_cgwb_frn cgwb_frn[MEMCG_CGWB_FRN_CNT]; #endif ^ permalink raw reply related [flat|nested] 4+ messages in thread
[parent not found: <an3-aksL0MZPM3ZJ@linux.dev>]
* Re: [linux-next:master] [mm/vmpressure] ea928e9e18: stress-ng.mremap.ops_per_sec 36.2% regression [not found] ` <an3-aksL0MZPM3ZJ@linux.dev> @ 2026-08-14 10:32 ` Usama Arif 0 siblings, 0 replies; 4+ messages in thread From: Usama Arif @ 2026-08-14 10:32 UTC (permalink / raw) To: Shakeel Butt Cc: kernel test robot, oe-lkp, lkp, Andrew Morton, David Hildenbrand, Johannes Weiner, Liam R. Howlett, Lorenzo Stoakes, Michal Hocko, Michal Koutný, Mike Rapoport, Roman Gushchin, Suren Baghdasaryan, Tejun Heo, Vlastimil Babka, linux-mm, cgroups On 13/08/2026 18:29, Shakeel Butt wrote: > On Thu, Aug 13, 2026 at 06:14:50PM +0100, Usama Arif wrote: >> >> >> On 13/08/2026 18:01, Shakeel Butt wrote: >>> On Thu, Aug 13, 2026 at 09:16:22PM +0800, kernel test robot wrote: >>>> >>>> >>>> Hello, >>>> >>>> kernel test robot noticed a 36.2% regression of stress-ng.mremap.ops_per_sec on: >>>> >>>> commit: ea928e9e18da682e9a5bc40aa862bff7ce5ae42e ("mm/vmpressure: move v1 userspace eventfd code into memcontrol-v1.c") https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master >>>> >>>> in testcase: stress-ng >>>> version: stress-ng-x86_64-29ce10a2c-1_20260712 >>>> with following parameters: >>>> >>>> nr_threads: 100% >>>> testtime: 60s >>>> test: mremap >>>> cpufreq_governor: performance >>>> >>>> >>>> >>>> config: x86_64-rhel-9.4 (CONFIG_MEMCG=y and CONFIG_MEMCG_V1 is not set) >>>> compiler: gcc-14 >>>> test machine: 256 threads 4 sockets INTEL(R) XEON(R) PLATINUM 8592+ (Emerald Rapids) with 256G memory >>>> >>>> (please refer to attached dmesg/kmsg for entire log/backtrace) >>>> >>> >>> Hi there, >>> >>> Can you please test the following patch and see if it fixes the regression? >>> >>> >>> From 84c0b05b3bc5cf73ee66ead75aafb1ad684462c3 Mon Sep 17 00:00:00 2001 >>> From: Shakeel Butt <shakeel.butt@linux.dev> >>> Date: Thu, 13 Aug 2026 09:38:28 -0700 >>> Subject: [PATCH] memcg: keep vmstats_percpu off the memory_events[] cacheline >>> >>> Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev> >>> --- >>> include/linux/memcontrol.h | 10 ++++++---- >>> 1 file changed, 6 insertions(+), 4 deletions(-) >>> >>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h >>> index e78bc98ab229..e25d5b9a1db8 100644 >>> --- a/include/linux/memcontrol.h >>> +++ b/include/linux/memcontrol.h >>> @@ -246,8 +246,13 @@ struct mem_cgroup { >>> /* handle for "memory.swap.events" */ >>> struct cgroup_file swap_events_file; >>> >>> - /* memory.stat */ >>> + /* Read-mostly. */ >>> struct memcg_vmstats *vmstats; >>> + struct memcg_vmstats_percpu __percpu *vmstats_percpu; >>> + int kmemcg_id; >>> + >>> + /* Write-hot from here on; do not let it share with the above. */ >>> + CACHELINE_PADDING(_pad_); >>> >>> /* memory.events */ >>> atomic_long_t memory_events[MEMCG_NR_MEMORY_EVENTS]; >>> @@ -266,9 +271,6 @@ struct mem_cgroup { >>> #if BITS_PER_LONG < 64 >>> seqlock_t socket_pressure_seqlock; >>> #endif >>> - int kmemcg_id; >>> - >>> - struct memcg_vmstats_percpu __percpu *vmstats_percpu; >>> >>> #ifdef CONFIG_CGROUP_WRITEBACK >>> struct list_head cgwb_list; >> >> >> I was currently testing this diff, not sure which one would be better. > > I was just checking if false sharing of vmstats_percpu is the cause. If your > patch does not increase the struct size, we can go with that as a backportable > fix. I am planning to rearrange fields of struct mem_cgroup more drastically and > have it more stable as future work as we continuously see these regressions keep > popping up. > Yes this makes sense. I did not expect such a big change in a benchmark with my patch, although I feel like the microbenchmark is probably not that realistic. I think another issue is that its a 4 socket system. I only have access to a single socket system, and I see a 4.38% regression. Do you know if there a way for kernel test robot to test the below patch on its host? From b862e84e7bd6a54b1546b7f21a6cf991253def18 Mon Sep 17 00:00:00 2001 From: Usama Arif <usama.arif@linux.dev> Date: Thu, 13 Aug 2026 11:42:05 -0700 Subject: [PATCH] mm/memcontrol: avoid false sharing between vmstats and events Moving v1 userspace eventfd handling into memcontrol-v1.c shrank struct vmpressure from 112 to 24 bytes when CONFIG_MEMCG_V1 is disabled. This moved memory_events_local[MEMCG_SWAP_FAIL] and the hot vmstats_percpu pointer onto the same cacheline. The stress-ng mremap stressor exercises MADV_PAGEOUT with swap disabled, generating about 20 million MEMCG_SWAP_FAIL updates per 60-second run on a 176-CPU test system. Those writes bounce the line while memcg statistics paths load vmstats_percpu. Move cgwb_list into the existing alignment gap and cacheline-align vmstats_percpu. This separates the pointer from the event counters without increasing the size of struct mem_cgroup in the tested configuration. The blamed commit reduced median mremap throughput by 4.38% on the test system with one socket. The patched kernel brings the performance to within 0.5% of the parent which is within the observed boot-to-boot spread (up to 1.2%). Fixes: ea928e9e18da ("mm/vmpressure: move v1 userspace eventfd code into memcontrol-v1.c") Reported-by: kernel test robot <yi1.lai@intel.com> Closes: https://lore.kernel.org/oe-lkp/202608131743.c6a7dda4-lkp@intel.com Signed-off-by: Usama Arif <usama.arif@linux.dev> --- include/linux/memcontrol.h | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index e78bc98ab229b..215e2e87f42b2 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -268,10 +268,15 @@ struct mem_cgroup { #endif int kmemcg_id; - struct memcg_vmstats_percpu __percpu *vmstats_percpu; - #ifdef CONFIG_CGROUP_WRITEBACK struct list_head cgwb_list; +#endif + + /* Keep the hot per-CPU stats pointer away from memory event counters. */ + struct memcg_vmstats_percpu __percpu *vmstats_percpu + ____cacheline_aligned_in_smp; + +#ifdef CONFIG_CGROUP_WRITEBACK struct wb_domain cgwb_domain; struct memcg_cgwb_frn cgwb_frn[MEMCG_CGWB_FRN_CNT]; #endif -- 2.53.0-Meta >> >> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h >> index e78bc98ab229b..215e2e87f42b2 100644 >> --- a/include/linux/memcontrol.h >> +++ b/include/linux/memcontrol.h >> @@ -268,10 +268,15 @@ struct mem_cgroup { >> #endif >> int kmemcg_id; >> >> - struct memcg_vmstats_percpu __percpu *vmstats_percpu; >> - >> #ifdef CONFIG_CGROUP_WRITEBACK >> struct list_head cgwb_list; >> +#endif >> + >> + /* Keep the hot per-CPU stats pointer away from memory event counters. */ >> + struct memcg_vmstats_percpu __percpu *vmstats_percpu >> + ____cacheline_aligned_in_smp; >> + >> +#ifdef CONFIG_CGROUP_WRITEBACK >> struct wb_domain cgwb_domain; >> struct memcg_cgwb_frn cgwb_frn[MEMCG_CGWB_FRN_CNT]; >> #endif >> ^ permalink raw reply related [flat|nested] 4+ messages in thread
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2026-08-13 13:16 [linux-next:master] [mm/vmpressure] ea928e9e18: stress-ng.mremap.ops_per_sec 36.2% regression kernel test robot
2026-08-13 17:01 ` Shakeel Butt
2026-08-13 17:14 ` Usama Arif
[not found] ` <an3-aksL0MZPM3ZJ@linux.dev>
2026-08-14 10:32 ` Usama Arif
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