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Fri, 26 Jan 2024 10:01:53 -0800 (PST) MIME-Version: 1.0 References: <20240126083015.3557006-1-chengming.zhou@linux.dev> In-Reply-To: <20240126083015.3557006-1-chengming.zhou@linux.dev> From: Nhat Pham Date: Fri, 26 Jan 2024 10:01:41 -0800 Message-ID: Subject: Re: [PATCH 1/2] mm/zswap: don't return LRU_SKIP if we have dropped lru lock To: chengming.zhou@linux.dev Cc: hannes@cmpxchg.org, yosryahmed@google.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Chengming Zhou Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 8744B18002A X-Stat-Signature: 4wfob4nsxokouozwi87snht7nag5jbyw X-HE-Tag: 1706292114-307513 X-HE-Meta: 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 a2Rdzdzs G/g6IV5Wua/QJjhUpaqRY93ksKKYdM3uD2YvPKXfzAcZK2iTc+QmBc9GyIHlc65H68TI2y4tdDCnp4+3LdpgezYJW6OhyQy1dsHvRxJGFdon5IK37jHFrFNcxiUWlsBvB8SUmyWZRoFXMzz+Fiswox8/BYcCW9p6rI5eA8+HecmrB/5bfdob8mPiHWTov724fnqBxtHuSvjbDG/y+gXaqe6F6MDHcY5X+Ikvem905YIBrWsn+CpAFTtlzZkqDVG/AnvxUoCTYBcOfG4Gq8VYZgM3T9BU7yrVnnkwZDGuk89BZPG92629oezizcWUzo6z/bSjQTcfG64ElrgjnI5x/EGeJylm3MqG6PJyy6EPE6nMRhJgxVzp4IdDT8A6uEYkBr18ENlstugXJi02yk6djrjd/6Sq3/NrxbOoIAMyqpkI/um5er0FB49XEmuemfFn5xrqRzmiFYV/8BlE3QtBhrh6slIVKtnPNBnxe X-Bogosity: Ham, tests=bogofilter, spamicity=0.000005, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jan 26, 2024 at 12:31=E2=80=AFAM wrote: > > From: Chengming Zhou > > LRU_SKIP can only be returned if we don't ever dropped lru lock, or > we need to return LRU_RETRY to restart from the head of lru list. Ooops. You're right! I just double checked and only LRU_REMOVED_RETRY and LRU_RETRY indicate we might have dropped the lock. My bad. > > Actually we may need to introduce another LRU_STOP to really terminate > the ongoing shrinking scan process, when we encounter a warm page Yup. This is what I was trying (and failing) to do. To be honest, this needs to be even stronger: short-circuit ALL concurrent/ongoing zswap shrinker scan processes that are touching this memcg (as they will also shrink into warmer regions going forward). But that's a bit more engineering to do. LRU_STOP, which stops this scan process, would be a good place to start. > already in the swap cache. The current list_lru implementation > doesn't have this function to early break from __list_lru_walk_one. > > Fixes: b5ba474f3f51 ("zswap: shrink zswap pool based on memory pressure") > Signed-off-by: Chengming Zhou Reviewed-by: Nhat Pham > --- > mm/zswap.c | 4 +--- > 1 file changed, 1 insertion(+), 3 deletions(-) > > diff --git a/mm/zswap.c b/mm/zswap.c > index 00e90b9b5417..81cb3790e0dd 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -901,10 +901,8 @@ static enum lru_status shrink_memcg_cb(struct list_h= ead *item, struct list_lru_o > * into the warmer region. We should terminate shrinking = (if we're in the dynamic > * shrinker context). > */ > - if (writeback_result =3D=3D -EEXIST && encountered_page_i= n_swapcache) { > - ret =3D LRU_SKIP; > + if (writeback_result =3D=3D -EEXIST && encountered_page_i= n_swapcache) > *encountered_page_in_swapcache =3D true; > - } > > goto put_unlock; > } > -- > 2.40.1 >