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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 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 X-Stat-Signature: 1n3qow5zrhmr3ucmhjzh1cidiaxsqi13 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 59F8F120019 X-Rspam-User: X-HE-Tag: 1700554091-81371 X-HE-Meta: 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 CL0rfuBd m7ZTsISGCaN2kW95EQG/uvoO7Fxnqw5NPlrL5ou+cJQbduwLjyeLhztjphF8Z9eeKHKBCONnyYLQmVR0GuHAOYhhS12aP7/xZcnu7um7pma2R+TCd15WD7TfYlpprYijws9HJ8CUX91ok9Gi6vbgW03c6Xg1fZCL2vRFdWlTtG7AHuaoInHAYsioqaz/IPijQX0CZTduz0sl1oi3yTKugS2B4gvqr25M+EVPyAFtX13Ovh4ZQ3hNJnACy8bDLSUrM7Fig3tGw3mxEiMJFYWBdp7P6qw== 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: 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=eDzMnT=9dZOT0dpMWcurHLr6Do+GA@mail.gmail.com/ [2]. https://lore.kernel.org/linux-mm/CAJD7tkafz_2XAuqE8tGLPEcpLngewhUo=5US14PAtSM9tLBUQg@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 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 Sachin. 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; + /* Swap space is exhausted, only reclaim swapcache for anon LRU */ + unsigned int swapcache_only:1; + /* Allocation order */ s8 order; @@ -308,10 +311,36 @@ static bool can_demote(int nid, struct scan_control *sc) return true; } +#ifdef CONFIG_SWAP +static bool can_reclaim_swapcache(struct mem_cgroup *memcg, int nid) +{ + struct pglist_data *pgdat = NODE_DATA(nid); + unsigned long nr_swapcache; + + if (!memcg) { + nr_swapcache = node_page_state(pgdat, NR_SWAPCACHE); + } else { + struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat); + + nr_swapcache = 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 = 0; + if (memcg == NULL) { /* * For non-memcg reclaim, is there @@ -330,7 +359,17 @@ static inline bool can_reclaim_anon_pages(struct mem_cgroup *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 = 1; + return true; + } + + return false; } /* @@ -1642,6 +1681,15 @@ static unsigned long isolate_lru_folios(unsigned long nr_to_scan, */ scan += nr_pages; + /* + * 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))