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Fri, 06 Oct 2023 14:40:59 -0700 (PDT) MIME-Version: 1.0 References: <20231006160024.170748-1-hannes@cmpxchg.org> In-Reply-To: <20231006160024.170748-1-hannes@cmpxchg.org> From: Nhat Pham Date: Fri, 6 Oct 2023 14:40:48 -0700 Message-ID: Subject: Re: [PATCH] mm: zswap: fix pool refcount bug around shrink_worker() To: Johannes Weiner Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Chris Mason , stable@vger.kernel.org, Vitaly Wool , Domenico Cerasuolo Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 69511180011 X-Rspam-User: X-Stat-Signature: pnrhjbnu7i84cn59er45ghtmdh74nnyq X-Rspamd-Server: rspam01 X-HE-Tag: 1696628460-294976 X-HE-Meta: U2FsdGVkX19zb9Uby7ZUfeN0rwQbSIndXwA5c8NADaAL5qiFuSPu9L9r0rHVze6Z2+QAM6XrrLUp4T0kBnOevIIUaHLA0yghrnvlYLNIMQ4vyNB9Ol7YoLNc71Qg5DmoQNkdB4YcVb/nCq8G4h3X0RMs0ZCLASG/S3etyUmJdTCktcOf6ygiUixBIuPlAXUgPmidIEu0OoZyyzC9pYjNY4AbwZ7LlAttcV9XWAATdP8fyVJVXu9chLJk1u98N6KT1rUuzuLgoDL3wScguSwoUVuzaog+5jZltunfAx9vfl1Pm5NTriD1aR3HM5T6BZQeGyItbs+hymaP7OWg9C44cClJ2L35AApZg0jH5KYTOPzZkOxPeMn8/8ltzkm2zFeayKTP7wdENntbo6PkJyuqBFPZQxOBdeS2qnf4MZG/piALAkYpkV2i7FGXlze2Xf+wo/bP304+5J/LzDZi8RZN6HqDE0pnYTAmUDXWxa5djs97grvSVsVbRnsNDxBjanWyeEiJr9iVSeak3HXLbkzjxhnxqrZYym7oOpYBXDNl1TXXwgWO/U5hDVj9w6S9A7jVvSnrWdu3neYs2/kouSqxPnwWTC0QRytReidepHQoep1poxgRryRGw8zCFpBpPolNjySjPSVkROZQ0i17k3WyEpbVWKo0zwfqaDxSUfoneOOkuqTuAG1uH3cyY3nXQaPX8MZcMwtUIUdyXkzjCpiuirn2+1FBOWIt9oT96bJUVSe7rbd1x6KIPPjTw0TkCc/4oc7Fp0qlzwY8I37kYttW5lPwKwwhCFu0bEeHjCQUPSGZ8KZ0cN6yDCEZwEZ3ApIVl/Y1fiQCXZKFlk2sNTASYAVVaRYKu1odIVB5Zlv8I05qd/dyPgFfRtFDOIvhvzw+Dy7T6OfnRGWm+5KBfsrvDPNYRdKqqhS7LC41keeMwq/rAkUE7Ul9O/HZA6E/15FOfRvGOFzKTj1BcgFzDAk m8221EBX 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000213, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Oct 6, 2023 at 9:00=E2=80=AFAM Johannes Weiner = wrote: > > When a zswap store fails due to the limit, it acquires a pool > reference and queues the shrinker. When the shrinker runs, it drops > the reference. However, there can be multiple store attempts before > the shrinker wakes up and runs once. This results in reference leaks > and eventual saturation warnings for the pool refcount. > > Fix this by dropping the reference again when the shrinker is already > queued. This ensures one reference per shrinker run. > > Reported-by: Chris Mason > Fixes: 45190f01dd40 ("mm/zswap.c: add allocation hysteresis if pool limit= is hit") > Cc: stable@vger.kernel.org [5.6+] > Cc: Vitaly Wool > Cc: Domenico Cerasuolo > Cc: Nhat Pham > Signed-off-by: Johannes Weiner > --- > mm/zswap.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/zswap.c b/mm/zswap.c > index 083c693602b8..37d2b1cb2ecb 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -1383,8 +1383,8 @@ bool zswap_store(struct folio *folio) > > shrink: > pool =3D zswap_pool_last_get(); > - if (pool) > - queue_work(shrink_wq, &pool->shrink_work); > + if (pool && !queue_work(shrink_wq, &pool->shrink_work)) > + zswap_pool_put(pool); > goto reject; > } > > -- > 2.42.0 > Acked-by: Nhat Pham Random tangent: this asynchronous writeback mechanism is always kinda weird to me. We could have quite a bit of memory inversion before the shrinker finally kicks in and frees up zswap pool space. But I guess if it doesn't break then don't fix it. Maybe a shrinker that proactively writes pages back as memory pressure builds up could help ;)