Re: [PATCH v2 4/4] mm: zswap: mark the zswap shrinker SHRINKER_NONSLAB

[Johannes Weiner <hannes@cmpxchg.org>]

On Mon, Sep 07, 2026 at 07:01:11PM +0800, Qinyun Tan wrote:
> With kmem accounting disabled (cgroup.memory=nokmem), memcg reclaim
> never invokes the zswap shrinker: a cgroup under memory pressure does
> not write back its own zswapped pages to make room; they are only
> written back by global reclaim or once the global pool limit kicks in.
> 
> The zswap shrinker is registered memcg-aware but without
> SHRINKER_NONSLAB, so under nokmem it is treated as a slab shrinker:
> before commit 03375203e1da ("mm: do not allocate shrinker info with
> cgroup.memory=nokmem") it was skipped by the !memcg_kmem_online()
> check in shrink_slab_memcg(); since that commit it is demoted to
> non-memcg-aware at registration.  But the zswap shrinker is not a slab
> shrinker: it tracks zswap entries and resolves the owning memcg from
> the folio's objcg, independent of kmem accounting.
> 
> This was noticed by Michal during review of the patch "mm/list_lru:
> don't copy stale shrinker id from non-memcg-aware shrinkers" [1].
> 
> Mark it SHRINKER_NONSLAB so it keeps its memcg awareness and runs
> under memcg reclaim with nokmem.
> 
> [1] https://lore.kernel.org/lkml/697713c4-0857-485b-aba7-c74f37a3c8b4@linux.alibaba.com/
> 
> Fixes: b5ba474f3f51 ("zswap: shrink zswap pool based on memory pressure")
> Suggested-by: Michal Koutný <mkoutny@suse.com>
> Signed-off-by: Qinyun Tan <qinyuntan@linux.alibaba.com>
> Acked-by: Usama Arif <usama.arif@linux.dev>

Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>