From d8c47cc7bf602ef73384a00869a70148146c1191 Mon Sep 17 00:00:00 2001 From: Johannes Weiner Date: Tue, 22 Mar 2022 14:46:30 -0700 Subject: mm: page_io: fix psi memory pressure error on cold swapins Once upon a time, all swapins counted toward memory pressure[1]. Then Joonsoo introduced workingset detection for anonymous pages and we gained the ability to distinguish hot from cold swapins[2][3]. But we failed to update swap_readpage() accordingly, and now we account partial memory pressure in the swapin path of cold memory. Not for all situations - which adds more inconsistency: paths using the conventional submit_bio() and lock_page() route will not see much pressure - unless storage itself is heavily congested and the bio submissions stall. ZRAM and ZSWAP do most of the work directly from swap_readpage() and will see all swapins reflected as pressure. IOW, a workload doing cold swapins could see little to no pressure reported with on-disk swap, but potentially high pressure with a zram or zswap backend. That confuses any psi-based health monitoring, load shedding, proactive reclaim, or userspace OOM killing schemes that might be in place for the workload. Restore consistency by making all swapin stall accounting conditional on the page actually being part of the workingset. [1] commit 937790699be9 ("mm/page_io.c: annotate refault stalls from swap_readpage") [2] commit aae466b0052e ("mm/swap: implement workingset detection for anonymous LRU") [3] commit cad8320b4b39 ("mm/swap: don't SetPageWorkingset unconditionally during swapin") Link: https://lkml.kernel.org/r/20220214214921.419687-1-hannes@cmpxchg.org Signed-off-by: Johannes Weiner Reported-by: CGEL Acked-by: Minchan Kim Cc: Joonsoo Kim Cc: Yu Zhao Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_io.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'mm/page_io.c') diff --git a/mm/page_io.c b/mm/page_io.c index 0bf8e40f4e57..5dd4dc2e2864 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -359,6 +359,7 @@ int swap_readpage(struct page *page, bool synchronous) struct bio *bio; int ret = 0; struct swap_info_struct *sis = page_swap_info(page); + bool workingset = PageWorkingset(page); unsigned long pflags; VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page); @@ -370,7 +371,8 @@ int swap_readpage(struct page *page, bool synchronous) * or the submitting cgroup IO-throttled, submission can be a * significant part of overall IO time. */ - psi_memstall_enter(&pflags); + if (workingset) + psi_memstall_enter(&pflags); delayacct_swapin_start(); if (frontswap_load(page) == 0) { @@ -433,7 +435,8 @@ int swap_readpage(struct page *page, bool synchronous) bio_put(bio); out: - psi_memstall_leave(&pflags); + if (workingset) + psi_memstall_leave(&pflags); delayacct_swapin_end(); return ret; } -- cgit v1.2.3