Re: [PATCH] mm/memcontrol: avoid false sharing between vmstats and events

[Shakeel Butt <shakeel.butt@linux.dev>]

On Mon, Aug 17, 2026 at 10:43:40AM -0700, Andrew Morton wrote:
> On Mon, 17 Aug 2026 03:38:35 -0700 Usama Arif <usama.arif@linux.dev> wrote:
> 
> > 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%).
> 
> Cool, thanks.
> 
> > Fixes: ea928e9e18da ("mm/vmpressure: move v1 userspace eventfd code into memcontrol-v1.c")
> 
> That's in mm-stable so I'll squeeze this fix into next week's 7.3-rc1
> merge pile.

Thanks Andrew. We should also add the following tag due to http://lore.kernel.org/aoAABX59IzUXz/Rv@ly-workstation

Tested-by: kernel test robot <yi1.lai@intel.com>
> 
>