From nobody Wed Dec 17 04:12:42 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 48B9CC5ACB3 for ; Tue, 21 Nov 2023 08:08:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229516AbjKUIIP (ORCPT ); Tue, 21 Nov 2023 03:08:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38234 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229441AbjKUIIN (ORCPT ); Tue, 21 Nov 2023 03:08:13 -0500 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C1D70BB for ; Tue, 21 Nov 2023 00:08:08 -0800 (PST) Received: from dggpemd200004.china.huawei.com (unknown [172.30.72.54]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4SZH3B6frYz1P8cb; Tue, 21 Nov 2023 16:04:38 +0800 (CST) Received: from huawei.com (10.175.113.32) by dggpemd200004.china.huawei.com (7.185.36.141) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.2.1258.28; Tue, 21 Nov 2023 16:08:05 +0800 From: Liu Shixin To: Yu Zhao , Andrew Morton , Yosry Ahmed , Huang Ying , Sachin Sant , Michal Hocko , Johannes Weiner , Kefeng Wang CC: , , Liu Shixin Subject: [PATCH v10] mm: vmscan: try to reclaim swapcache pages if no swap space Date: Tue, 21 Nov 2023 17:06:24 +0800 Message-ID: <20231121090624.1814733-1-liushixin2@huawei.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Originating-IP: [10.175.113.32] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To dggpemd200004.china.huawei.com (7.185.36.141) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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]. By the way, since there are enough times of memory reclaim before OOM, it is not need to isolate too much swapcache pages in one times. [1]. https://lore.kernel.org/lkml/CAJD7tkZAfgncV+KbKr36=3DeDzMnT=3D9dZOT0dp= MWcurHLr6Do+GA@mail.gmail.com/ [2]. https://lore.kernel.org/linux-mm/CAJD7tkafz_2XAuqE8tGLPEcpLngewhUo=3D5= US14PAtSM9tLBUQg@mail.gmail.com/ Signed-off-by: Liu Shixin Tested-by: Yosry Ahmed Reviewed-by: "Huang, Ying" Reviewed-by: Yosry Ahmed --- v9->v10: Use per-node swapcache suggested by Yu Zhao. v8->v9: Move the swapcache check after can_demote() and refector=20 can_reclaim_anon_pages() a bit. v7->v8: Reset swapcache_only at the beginning of can_reclaim_anon_pages(). v6->v7: Reset swapcache_only to zero after there are swap spaces. v5->v6: Fix NULL pointing derefence and hung task problem reported by Sachi= n. mm/vmscan.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 49 insertions(+), 1 deletion(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 506f8220c5fe..1fcc94717370 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -136,6 +136,9 @@ struct scan_control { /* Always discard instead of demoting to lower tier memory */ unsigned int no_demotion:1; =20 + /* Swap space is exhausted, only reclaim swapcache for anon LRU */ + unsigned int swapcache_only:1; + /* Allocation order */ s8 order; =20 @@ -308,10 +311,36 @@ static bool can_demote(int nid, struct scan_control *= sc) return true; } =20 +#ifdef CONFIG_SWAP +static bool can_reclaim_swapcache(struct mem_cgroup *memcg, int nid) +{ + struct pglist_data *pgdat =3D NODE_DATA(nid); + unsigned long nr_swapcache; + + if (!memcg) { + nr_swapcache =3D node_page_state(pgdat, NR_SWAPCACHE); + } else { + struct lruvec *lruvec =3D mem_cgroup_lruvec(memcg, pgdat); + + nr_swapcache =3D lruvec_page_state_local(lruvec, NR_SWAPCACHE); + } + + return nr_swapcache > 0; +} +#else +static bool can_reclaim_swapcache(struct mem_cgroup *memcg, int nid) +{ + return false; +} +#endif + static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg, int nid, struct scan_control *sc) { + if (sc) + sc->swapcache_only =3D 0; + if (memcg =3D=3D NULL) { /* * For non-memcg reclaim, is there @@ -330,7 +359,17 @@ static inline bool can_reclaim_anon_pages(struct mem_c= group *memcg, * * Can it be reclaimed from this node via demotion? */ - return can_demote(nid, sc); + if (can_demote(nid, sc)) + return true; + + /* Is there any swapcache pages to reclaim in this node? */ + if (can_reclaim_swapcache(memcg, nid)) { + if (sc) + sc->swapcache_only =3D 1; + return true; + } + + return false; } =20 /* @@ -1642,6 +1681,15 @@ static unsigned long isolate_lru_folios(unsigned lon= g nr_to_scan, */ scan +=3D nr_pages; =20 + /* + * Count non-swapcache too because the swapcache pages may + * be rare and it takes too much times here if not count + * the non-swapcache pages. + */ + if (unlikely(sc->swapcache_only && !is_file_lru(lru) && + !folio_test_swapcache(folio))) + goto move; + if (!folio_test_lru(folio)) goto move; if (!sc->may_unmap && folio_mapped(folio)) --=20 2.25.1