Re: [PATCH v3 0/4] mm: restore per-memcg reclaim for NONSLAB shrinkers under nokmem

[Qinyun Tan <qinyuntan@linux.alibaba.com>]

On 9/11/26 6:34 AM, Andrew Morton wrote:
> On Thu, 10 Sep 2026 16:07:18 +0800 Qinyun Tan <qinyuntan@linux.alibaba.com> wrote:
> 
>> With cgroup.memory=nokmem, the THP deferred split shrinker and the
>> zswap shrinker are degraded in two ways.
>>
>> First, both shrinkers are missing the SHRINKER_NONSLAB flag, so
>> shrinker_memcg_alloc() demotes them to non-memcg-aware shrinkers:
>> limit-induced reclaim of a cgroup neither splits its partially
>> unmapped THPs nor writes back its zswapped pages.  v1 of this series
>> [1] restored the flag to fix that.
>>
>> However, as Sashiko's review of v1 pointed out [2], the flag alone
>> is not enough.  __list_lru_init() also collapses every list_lru into
>> per-node lists under nokmem, so even with the flag restored, the
>> objects of all cgroups share one list per node: the per-memcg
>> shrinker bit is only set for whichever memcg happens to repopulate
>> the empty list, so pressure in other cgroups may not even trigger
>> the scan, and when it does, the scan walks everyone's objects.
>>
>> Before commit fafaeceb89a5 ("mm: switch deferred split shrinker to
>> list_lru"), THP had fully per-memcg deferred split queues embedded
>> in struct mem_cgroup, working independently of kmem accounting.
>> nokmem only opts out of kernel slab accounting; THPs and zswapped
>> pages are user memory and remain charged to their cgroups, so
>> per-memcg reclaim is still what these shrinkers want.
>>
>> This series keeps list_lrus backed by SHRINKER_NONSLAB shrinkers
>> memcg aware under nokmem:
> 
> Thanks.
> 
> It seems that Sashiko still doesn't understand that memory allocations
> in __init code are considered "can't fail".
> 
> 	https://sashiko.dev/#/patchset/20260910080722.3961351-1-qinyuntan@linux.alibaba.com
> 
> otoh, failures in the functiond which hugepage_init() calls might be
> caused by things other than ENOMEM so I guess we shouldn't zap all that
> cleanup code.
> 
> Anyway, that's unrelated to your changes.
> 
> I'll save this patchset away for later and shall await reviewer input. 
> Please poke me in a week or so if there hasn't been any, Things are
> crazy lately.

Hi Andrew,
 
Thanks for your time looking into this series. A gentle ping, as you
suggested. Please let me know if anything else is needed from my side.

Thanks,
Qinyun Tan