Re: [PATCH v3 3/3] mm: shmem: make unused huge shrinker memcg aware

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 8/3/26 4:46 PM, Qi Zheng wrote:
> From: Qi Zheng <zhengqi.arch@bytedance.com>
> 
> The shmem unused huge shrinker keeps a per-superblock list of inodes whose
> tail huge folio extends beyond i_size. Since that list is not memcg aware,
> reclaim triggered by one memcg can scan inodes from the whole superblock
> and split shmem huge folios charged to unrelated memcgs.
> 
> Convert the shrink list to a memcg-aware list_lru. Queue each inode on the
> list_lru sublist matching the memcg and node of the current tail huge
> folio, so non-root memcg reclaim only walks candidates charged to the
> reclaiming memcg. Global reclaim, root memcg reclaim and shmem quota
> reclaim keep global semantics.
> 
> The list_lru still tracks inodes while the actual split target is the
> current tail huge folio, so validate the folio memcg/node during scan. If
> the folio no longer matches the reclaim context or splitting cannot
> proceed, requeue the inode according to the current tail folio; if the
> inode is no longer shrinkable, drop the scan entry.
> 
> This can be tested with the shrinker debugfs interface by allocating 32
> tmpfs tail THPs in each of two memcgs, then scanning the sb-tmpfs shrinker
> with memcg A's cgroup id:
> 
>                 before A scan    after A scan
>    base         A=64M, B=64M     A=64M, B=64M (per-memcg count is skipped)
>    patched      A=64M, B=64M     A=0,   B=64M
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---

Apart from the two issues Sashiko pointed out (which you've already 
replied to), nothing else jumped out at me. Thanks.