linux-kernel - [PATCH v3] mm: vmscan: try to reclaim swapcache pages if no swap space

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Date:   Sat, 26 Aug 2023 11:44:01 +0800
From:   Liu Shixin <liushixin2@...wei.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>,
        Huang Ying <ying.huang@...el.com>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        <wangkefeng.wang@...wei.com>
CC:     <linux-kernel@...r.kernel.org>, <cgroups@...r.kernel.org>,
        <linux-mm@...ck.org>, Liu Shixin <liushixin2@...wei.com>
Subject: [PATCH v3] mm: vmscan: try to reclaim swapcache pages if no swap space

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.

This problem can be fixed by checking number of swapcache pages in
can_reclaim_anon_pages().

Add a new bit swapcache_only in struct scan_control to skip isolating anon
pages that are not in the swap cache when only swap cache can be reclaimed.

Signed-off-by: Liu Shixin <liushixin2@...wei.com>
---
 include/linux/swap.h |  6 ++++++
 mm/memcontrol.c      |  8 ++++++++
 mm/vmscan.c          | 29 +++++++++++++++++++++++++++--
 3 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 456546443f1f..0318e918bfa4 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -669,6 +669,7 @@ 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)
@@ -691,6 +692,11 @@ 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 e8ca4bdcb03c..c465829db92b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -7567,6 +7567,14 @@ 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 7c33c5b653ef..5cb4adf6642b 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;
 
@@ -613,10 +616,20 @@ static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg,
 		 */
 		if (get_nr_swap_pages() > 0)
 			return true;
+		/* Is there any swapcache pages to reclaim? */
+		if (total_swapcache_pages() > 0) {
+			sc->swapcache_only = 1;
+			return true;
+		}
 	} else {
 		/* Is the memcg below its swap limit? */
 		if (mem_cgroup_get_nr_swap_pages(memcg) > 0)
 			return true;
+		/* Is there any swapcache pages in memcg to reclaim? */
+		if (mem_cgroup_get_nr_swapcache_pages(memcg) > 0) {
+			sc->swapcache_only = 1;
+			return true;
+		}
 	}
 
 	/*
@@ -2280,6 +2293,19 @@ static bool skip_cma(struct folio *folio, struct scan_control *sc)
 }
 #endif
 
+static bool skip_isolate(struct folio *folio, struct scan_control *sc,
+			 enum lru_list lru)
+{
+	if (folio_zonenum(folio) > sc->reclaim_idx)
+		return true;
+	if (skip_cma(folio, sc))
+		return true;
+	if (unlikely(sc->swapcache_only && !is_file_lru(lru) &&
+	    !folio_test_swapcache(folio)))
+		return true;
+	return false;
+}
+
 /*
  * Isolating page from the lruvec to fill in @dst list by nr_to_scan times.
  *
@@ -2326,8 +2352,7 @@ static unsigned long isolate_lru_folios(unsigned long nr_to_scan,
 		nr_pages = folio_nr_pages(folio);
 		total_scan += nr_pages;
 
-		if (folio_zonenum(folio) > sc->reclaim_idx ||
-				skip_cma(folio, sc)) {
+		if (skip_isolate(folio, sc, lru)) {
 			nr_skipped[folio_zonenum(folio)] += nr_pages;
 			move_to = &folios_skipped;
 			goto move;
-- 
2.25.1