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Sat, 4 Nov 2023 21:04:17 +0800 From: Liu Shixin To: Andrew Morton , Yosry Ahmed , Huang Ying , Sachin Sant , Michal Hocko , Johannes Weiner , Kefeng Wang CC: , , Liu Shixin Subject: [PATCH v7] mm: vmscan: try to reclaim swapcache pages if no swap space Date: Sat, 4 Nov 2023 22:03:13 +0800 Message-ID: <20231104140313.3418001-1-liushixin2@huawei.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 X-Originating-IP: [10.175.113.32] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To dggpemd200004.china.huawei.com (7.185.36.141) X-CFilter-Loop: Reflected X-Stat-Signature: n3g8q7khdud4kexjxppwrj15hnetw6ni X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 4A023C0026 X-Rspam-User: X-HE-Tag: 1699104314-975283 X-HE-Meta: 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 rWbI8VwU KiCkOVpTDWlvy/pNQuXSda0KqYRKj9Q0U7gyyW9aCW6mLvIfoQgtsH3k/+FL00lwVtPLKAlvu9mJB+eUwo5GwkOh7np71mi1y77/SXXNLFtuf5uuJ0JkmN/ZQu4lzNz6B8bArp7zzMpVVSQmzexwSYJJTA7DYLe693cjH/FTSZBTMebCqqagZtkzAg4ziFf2sZUFGsy6yFIZVWLFr9KhSRt3CAPs0SZmnpojMABDeQgxMx9TLRBmMSH4L1S6eA2Cw+8LOiQbBrrlrGp5FrnwP9bkgHA== 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 --- 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. include/linux/swap.h | 6 ++++++ mm/memcontrol.c | 8 ++++++++ mm/vmscan.c | 36 ++++++++++++++++++++++++++++++++++-- 3 files changed, 48 insertions(+), 2 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index f6dd6575b905..3ba146ae7cf5 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -659,6 +659,7 @@ static inline void mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_p } extern long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg); +extern long mem_cgroup_get_nr_swapcache_pages(struct mem_cgroup *memcg); extern bool mem_cgroup_swap_full(struct folio *folio); #else static inline void mem_cgroup_swapout(struct folio *folio, swp_entry_t entry) @@ -681,6 +682,11 @@ static inline long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg) return get_nr_swap_pages(); } +static inline long mem_cgroup_get_nr_swapcache_pages(struct mem_cgroup *memcg) +{ + return total_swapcache_pages(); +} + static inline bool mem_cgroup_swap_full(struct folio *folio) { return vm_swap_full(); diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 5b009b233ab8..29e34c06ca83 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -7584,6 +7584,14 @@ long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg) return nr_swap_pages; } +long mem_cgroup_get_nr_swapcache_pages(struct mem_cgroup *memcg) +{ + if (mem_cgroup_disabled()) + return total_swapcache_pages(); + + return memcg_page_state(memcg, NR_SWAPCACHE); +} + bool mem_cgroup_swap_full(struct folio *folio) { struct mem_cgroup *memcg; diff --git a/mm/vmscan.c b/mm/vmscan.c index 6f13394b112e..a5e04291662f 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -137,6 +137,9 @@ 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; @@ -602,6 +605,12 @@ static bool can_demote(int nid, struct scan_control *sc) return true; } +static void set_swapcache_mode(struct scan_control *sc, bool swapcache_only) +{ + if (sc) + sc->swapcache_only = swapcache_only; +} + static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg, int nid, struct scan_control *sc) @@ -611,12 +620,26 @@ static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg, * For non-memcg reclaim, is there * space in any swap device? */ - if (get_nr_swap_pages() > 0) + if (get_nr_swap_pages() > 0) { + set_swapcache_mode(sc, false); return true; + } + /* Is there any swapcache pages to reclaim? */ + if (total_swapcache_pages() > 0) { + set_swapcache_mode(sc, true); + return true; + } } else { /* Is the memcg below its swap limit? */ - if (mem_cgroup_get_nr_swap_pages(memcg) > 0) + if (mem_cgroup_get_nr_swap_pages(memcg) > 0) { + set_swapcache_mode(sc, false); return true; + } + /* Is there any swapcache pages in memcg to reclaim? */ + if (mem_cgroup_get_nr_swapcache_pages(memcg) > 0) { + set_swapcache_mode(sc, true); + return true; + } } /* @@ -2342,6 +2365,15 @@ 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))