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zsmalloc: return -EBUSY for zspage migration lock contention

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movable_operations::migrate_page() should return an appropriate error code
for temporary migration failures so the migration core can handle them
correctly.

zs_page_migrate() currently returns -EINVAL when zspage_write_trylock()
fails.  That path reflects transient lock contention, not invalid input,
so -EINVAL is clearly wrong.

However, -EAGAIN is also inappropriate here: the zspage's reader-lock
owner may hold the lock for an unbounded duration due to slow
decompression or reader-lock owner preemption.  Since migration retries
are bounded by NR_MAX_MIGRATE_PAGES_RETRY and performed with virtually no
delay between attempts, there is no guarantee the lock will be released in
time for a retry to succeed.  -EAGAIN implies "try again soon", which does
not hold in this case.

Return -EBUSY instead, which more accurately conveys that the resource is
occupied and migration cannot proceed at this time.

Link: https://lkml.kernel.org/r/20260319065924.69337-1-hui.zhu@linux.dev
Signed-off-by: teawater <zhuhui@kylinos.cn>
Acked-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
teawater 2026-03-19 14:59:24 +08:00 committed by Andrew Morton
parent 6ebf98d71f
commit dc711106a0
1 changed files with 13 additions and 1 deletions
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14
mm/zsmalloc.c
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@ -1727,7 +1727,19 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
if (!zspage_write_trylock(zspage)) {
spin_unlock(&class->lock);
write_unlock(&pool->lock);
return -EINVAL;
/*
* Return -EBUSY but not -EAGAIN: the zspage's reader-lock
* owner may hold the lock for an unbounded duration due to a
* slow decompression or reader-lock owner preemption.
* Since migration retries are bounded by
* NR_MAX_MIGRATE_PAGES_RETRY and performed with virtually no
* delay between attempts, there is no guarantee the lock will
* be released in time for a retry to succeed.
* -EAGAIN implies "try again soon", which does not hold here.
* -EBUSY more accurately conveys "resource is occupied,
* migration cannot proceed".
*/
return -EBUSY;
}
/* We're committed, tell the world that this is a Zsmalloc page. */