Re: [PATCH mm-new v3] mm/memcontrol: Add memory.stat_refresh for on-demand stats flushing

[Leon Huang Fu <leon.huangfu@shopee.com>]

On Mon, Nov 10, 2025 at 7:28 PM Michal Hocko <mhocko@suse.com> wrote:
>
> On Mon 10-11-25 18:19:48, Leon Huang Fu wrote:
> > Memory cgroup statistics are updated asynchronously with periodic
> > flushing to reduce overhead. The current implementation uses a flush
> > threshold calculated as MEMCG_CHARGE_BATCH * num_online_cpus() for
> > determining when to aggregate per-CPU memory cgroup statistics. On
> > systems with high core counts, this threshold can become very large
> > (e.g., 64 * 256 = 16,384 on a 256-core system), leading to stale
> > statistics when userspace reads memory.stat files.
> >
> > This is particularly problematic for monitoring and management tools
> > that rely on reasonably fresh statistics, as they may observe data
> > that is thousands of updates out of date.
> >
> > Introduce a new write-only file, memory.stat_refresh, that allows
> > userspace to explicitly trigger an immediate flush of memory statistics.
> > Writing any value to this file forces a synchronous flush via
> > __mem_cgroup_flush_stats(memcg, true) for the cgroup and all its
> > descendants, ensuring that subsequent reads of memory.stat and
> > memory.numa_stat reflect current data.
> >
> > This approach follows the pattern established by /proc/sys/vm/stat_refresh
> > and memory.peak, where the written value is ignored, keeping the
> > interface simple and consistent with existing kernel APIs.
> >
> > Usage example:
> >   echo 1 > /sys/fs/cgroup/mygroup/memory.stat_refresh
> >   cat /sys/fs/cgroup/mygroup/memory.stat
> >
> > The feature is available in both cgroup v1 and v2 for consistency.
> >
> > Signed-off-by: Leon Huang Fu <leon.huangfu@shopee.com>
>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Thanks!
>

Thank you for your review.

Thanks,
Leon

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