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

[Qi Zheng]

On 8/6/26 1:35 PM, Baolin Wang wrote:
> On 8/3/26 4:46 PM, Qi Zheng wrote:
> > From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxxx>
> > ---
>
> Apart from the two issues Sashiko pointed out (which you've already 
> replied to), nothing else jumped out at me. Thanks.

Thanks for the review! I will fix those two issues as I replied, and
then send out v4.