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-rw-r--r--mm/memcontrol.c14
1 files changed, 13 insertions, 1 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7fdc001ce15f..2db2aeac8a9e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6748,7 +6748,19 @@ int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask)
memcg_check_events(memcg, page);
local_irq_enable();
- if (PageSwapCache(page)) {
+ /*
+ * Cgroup1's unified memory+swap counter has been charged with the
+ * new swapcache page, finish the transfer by uncharging the swap
+ * slot. The swap slot would also get uncharged when it dies, but
+ * it can stick around indefinitely and we'd count the page twice
+ * the entire time.
+ *
+ * Cgroup2 has separate resource counters for memory and swap,
+ * so this is a non-issue here. Memory and swap charge lifetimes
+ * correspond 1:1 to page and swap slot lifetimes: we charge the
+ * page to memory here, and uncharge swap when the slot is freed.
+ */
+ if (do_memsw_account() && PageSwapCache(page)) {
swp_entry_t entry = { .val = page_private(page) };
/*
* The swap entry might not get freed for a long time,