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

[Qi Zheng <qi.zheng@linux.dev>]

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@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.

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