From cad8320b4b395702e49578580c70026c8271ea88 Mon Sep 17 00:00:00 2001 From: Yu Zhao Date: Wed, 24 Feb 2021 12:03:08 -0800 Subject: mm/swap: don't SetPageWorkingset unconditionally during swapin We are capable of SetPageWorkingset based on refault distances after commit aae466b0052e ("mm/swap: implement workingset detection for anonymous LRU"). This is done by workingset_refault(), which is right above the unconditional SetPageWorkingset deleted by this patch. The unconditional SetPageWorkingset miscategorizes pages that are read ahead or never belonged to the working set (e.g., tmpfs pages accessed only once by fd). When those pages are swapped in (after they were swapped out) for the first time, they skew PSI (when using async swap). When this happens again, depending on their refault distances, they might skew workingset_restore_anon counter in addition to PSI because their shadows indicate they were part of the working set. Historically, SetPageWorkingset was added as part of the PSI series, and Johannes said: "It was meant to mark incoming pages under IO with SetPageWorkingset when waiting for them constituted a memory stall. On the page cache side, because we HAVE workingset detection, this was specific to recently evicted pages that had been active in their previous life. On the anon side, the aging algorithm had no distinction between workingset and sporadically used pages. Given the choice between a) no swapin stalls are pressure and b) all swapin stalls are pressure, I went with the latter in order to detect swap storms. The false positive case - high rate of swapin without severe memory pressure - was relatively unlikely, because we tried to avoid swapping until everything was completely on fire in the first place." Link: https://lkml.kernel.org/r/20201209012400.1771150-1-yuzhao@google.com Link: https://lkml.kernel.org/r/20201214231253.62313-1-yuzhao@google.com Signed-off-by: Yu Zhao Acked-by: Vlastimil Babka Acked-by: Johannes Weiner Acked-by: Joonsoo Kim Acked-by: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swap_state.c | 1 - 1 file changed, 1 deletion(-) (limited to 'mm/swap_state.c') diff --git a/mm/swap_state.c b/mm/swap_state.c index 3507c82b2ef1..807b00eae969 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -537,7 +537,6 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, workingset_refault(page, shadow); /* Caller will initiate read into locked page */ - SetPageWorkingset(page); lru_cache_add(page); *new_page_allocated = true; return page; -- cgit