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bh=ENH/10FZxHe1EFz0Z49wUOO+GPWUvmASlOlk4QldG+8=; b=rYdiJfglM2lxJkg5FvmnBmTB9K+CeB2vdLdsXpcRxh2qr/bixeKfsWAqNPzCtE8tOabYr5 op3ugt38ztywBKOM6/mBpAkFAVgHEHPulCGNMDWI0zyqvez++Y+/PCu2crL6BIAcdbx+Cm ejaViwHbrGGWHZN1x8dTv5NguMxLv20= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id C599E139FD; Tue, 21 Nov 2023 13:00:21 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id nqMrLeWpXGVkIgAAMHmgww (envelope-from ); Tue, 21 Nov 2023 13:00:21 +0000 Date: Tue, 21 Nov 2023 14:00:21 +0100 From: Michal Hocko To: Liu Shixin Cc: Yu Zhao , Andrew Morton , Yosry Ahmed , Huang Ying , Sachin Sant , Johannes Weiner , Kefeng Wang , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v10] mm: vmscan: try to reclaim swapcache pages if no swap space Message-ID: References: <20231121090624.1814733-1-liushixin2@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231121090624.1814733-1-liushixin2@huawei.com> X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 5B2121C0017 X-Stat-Signature: yawpkk86hf9w578z5namh96wrueauddb X-Rspam-User: X-HE-Tag: 1700571624-548554 X-HE-Meta: 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 ZWB67yhz V32lPz7ASQVRJUuO8LNV8BBzQtHbyO39P5IDfOrTiKrqjDHbXz0z1ytGXWeFji/qwu+EDFSs8O8P7s9Dl7ZT5GF0jvFfsV1TS4gx3o3yQsWrO6RzTx0i0His12AxPDlf/+OIW3e3FvQFh168vI5OKsmYO2c2x95Bw+NE5qCsiGnxFIfX/LdLgWjjDKNesqZR4IYE4 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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 Tue 21-11-23 17:06:24, Liu Shixin wrote: > When spaces of swap devices are exhausted, only file pages can be > reclaimed. But there are still some swapcache pages in anon lru list. > This can lead to a premature out-of-memory. > > The problem is found with such step: > > Firstly, set a 9MB disk swap space, then create a cgroup with 10MB > memory limit, then runs an program to allocates about 15MB memory. > > The problem occurs occasionally, which may need about 100 times [1]. > > Fix it by checking number of swapcache pages in can_reclaim_anon_pages(). > If the number is not zero, return true and set swapcache_only to 1. > When scan anon lru list in swapcache_only mode, non-swapcache pages will > be skipped to isolate in order to accelerate reclaim efficiency. > > However, in swapcache_only mode, the scan count still increased when scan > non-swapcache pages because there are large number of non-swapcache pages > and rare swapcache pages in swapcache_only mode, and if the non-swapcache > is skipped and do not count, the scan of pages in isolate_lru_folios() can > eventually lead to hung task, just as Sachin reported [2]. I find this paragraph really confusing! I guess what you meant to say is that a real swapcache_only is problematic because it can end up not making any progress, correct? AFAIU you have addressed that problem by making swapcache_only anon LRU specific, right? That would be certainly more robust as you can still reclaim from file LRUs. I cannot say I like that because swapcache_only is a bit confusing and I do not think we want to grow more special purpose reclaim types. Would it be possible/reasonable to instead put swapcache pages on the file LRU instead? -- Michal Hocko SUSE Labs