Re: [PATCH v4 1/2] ext4: fix shrinker scan budget accounting in ext4_es_scan()

[sashiko-bot@kernel.org]

> do_shrink_slab() reads count_objects() once per invocation to derive
> a one-shot scan budget, then calls scan_objects() repeatedly until
> that budget is exhausted or scan_objects() returns SHRINK_STOP.
> include/linux/shrinker.h documents that scan_objects() "should track
> its actual progress" in sc->nr_scanned, so do_shrink_slab() can tell
> when there is nothing left to examine and stop early.
> 
> ext4_es_scan() never updates sc->nr_scanned, so it defaults to the
> full sc->nr_to_scan on every call. do_shrink_slab() therefore always
> believes a full batch was examined, regardless of what __es_shrink()
> actually did, and keeps calling scan_objects() until the budget
> derived from the (possibly stale) percpu extent_status count is
> drained, even after sbi->s_es_list has nothing left to examine.
> 
> Make __es_shrink() report the number of extent_status objects it
> [ ... ]
>   after this patch    239                      1 (0.4%)
> 
> Fixes: 1ab6c4997e04 ("fs: convert fs shrinkers to new scan/count API")
> Cc: stable@vger.kernel.org
> Signed-off-by: Qiliang Yuan <odys.yuan@gmail.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20261001-fix-ext4-es-scan-nr-scanned-v4-0-b13703714ce2@gmail.com?part=1