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X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Nov 10, 2025 at 06:19:48PM +0800, 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 that is thousands of updates out of date.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 > --- > v2 -> v3: > - Flush stats by memory.stat_refresh (per Michal) > - https://lore.kernel.org/linux-mm/20251105074917.94531-1-leon.huangfu@shopee.com/ > > v1 -> v2: > - Flush stats when write the file (per Michal). > - https://lore.kernel.org/linux-mm/20251104031908.77313-1-leon.huangfu@shopee.com/ > > Documentation/admin-guide/cgroup-v2.rst | 21 +++++++++++++++++-- > mm/memcontrol-v1.c | 4 ++++ > mm/memcontrol-v1.h | 2 ++ > mm/memcontrol.c | 27 ++++++++++++++++++------- > 4 files changed, 45 insertions(+), 9 deletions(-) Hi Leon, I have a few questions on the patch. > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst > index 3345961c30ac..ca079932f957 100644 > --- a/Documentation/admin-guide/cgroup-v2.rst > +++ b/Documentation/admin-guide/cgroup-v2.rst > @@ -1337,7 +1337,7 @@ PAGE_SIZE multiple when read back. > cgroup is within its effective low boundary, the cgroup's > memory won't be reclaimed unless there is no reclaimable > memory available in unprotected cgroups. > - Above the effective low boundary (or > + Above the effective low boundary (or Is this whitespace change? it looks the same as before. > effective min boundary if it is higher), pages are reclaimed > proportionally to the overage, reducing reclaim pressure for > smaller overages. > @@ -1785,6 +1785,23 @@ The following nested keys are defined. > up if hugetlb usage is accounted for in memory.current (i.e. > cgroup is mounted with the memory_hugetlb_accounting option). > > + memory.stat_refresh > + A write-only file which exists on non-root cgroups. Why don't we create the file for the root cgroup? > + Writing any value to this file forces an immediate flush of > + memory statistics for this cgroup and its descendants. This > + ensures subsequent reads of memory.stat and memory.numa_stat > + reflect the most current data. > + > + This is useful on high-core count systems where per-CPU caching > + can lead to stale statistics, or when precise memory usage > + information is needed for monitoring or debugging purposes. > + > + Example:: > + > + echo 1 > memory.stat_refresh > + cat memory.stat > + > memory.numa_stat > A read-only nested-keyed file which exists on non-root cgroups. > > @@ -2173,7 +2190,7 @@ of the two is enforced. > > cgroup writeback requires explicit support from the underlying > filesystem. Currently, cgroup writeback is implemented on ext2, ext4, > -btrfs, f2fs, and xfs. On other filesystems, all writeback IOs are > +btrfs, f2fs, and xfs. On other filesystems, all writeback IOs are > attributed to the root cgroup. Same here, not sure what's changed... > There are inherent differences in memory and writeback management > diff --git a/mm/memcontrol-v1.h b/mm/memcontrol-v1.h > index 6358464bb416..a14d4d74c9aa 100644 > --- a/mm/memcontrol-v1.h > +++ b/mm/memcontrol-v1.h > @@ -4666,6 +4675,10 @@ static struct cftype memory_files[] = { > .name = "stat", > .seq_show = memory_stat_show, > }, > + { > + .name = "stat_refresh", > + .write = memory_stat_refresh_write, I think we should use the CFTYPE_NOT_ON_ROOT flag to avoid creating the file for the root cgroup if that's intended? -- Cheers, Harry / Hyeonggon > + }, > #ifdef CONFIG_NUMA > { > .name = "numa_stat", > -- > 2.51.2 > >