[merged mm-stable] zsmalloc-return-ebusy-for-zspage-migration-lock-contention.patch removed from -mm tree

Andrew Morton
2026-03-29T00:42:27Z

The quilt patch titled
Subject: zsmalloc: return -EBUSY for zspage migration lock contention
has been removed from the -mm tree. Its filename was
zsmalloc-return-ebusy-for-zspage-migration-lock-contention.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: teawater <zhuhui@kylinos.cn>
Subject: zsmalloc: return -EBUSY for zspage migration lock contention
Date: Thu, 19 Mar 2026 14:59:24 +0800

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>
---

mm/zsmalloc.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

--- a/mm/zsmalloc.c~zsmalloc-return-ebusy-for-zspage-migration-lock-contention
+++ a/mm/zsmalloc.c
@@ -1727,7 +1727,19 @@ static int zs_page_migrate(struct 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. */
_

Patches currently in -mm which might be from zhuhui@kylinos.cn are

mm-memcontrol-batch-memcg-charging-in-__memcg_slab_post_alloc_hook.patch