From 62fdb1632bcbed30c40f6bd2b58297617e442658 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Fri, 18 Sep 2020 21:20:03 -0700 Subject: [PATCH] ksm: reinstate memcg charge on copied pages Patch series "mm: fixes to past from future testing". Here's a set of independent fixes against 5.9-rc2: prompted by testing Alex Shi's "warning on !memcg" and lru_lock series, but I think fit for 5.9 - though maybe only the first for stable. This patch (of 5): In 5.8 some instances of memcg charging in do_swap_page() and unuse_pte() were removed, on the understanding that swap cache is now already charged at those points; but a case was missed, when ksm_might_need_to_copy() has decided it must allocate a substitute page: such pages were never charged. Fix it inside ksm_might_need_to_copy(). This was discovered by Alex Shi's prospective commit "mm/memcg: warning on !memcg after readahead page charged". But there is a another surprise: this also fixes some rarer uncharged PageAnon cases, when KSM is configured in, but has never been activated. ksm_might_need_to_copy()'s anon_vma->root and linear_page_index() check sometimes catches a case which would need to have been copied if KSM were turned on. Or that's my optimistic interpretation (of my own old code), but it leaves some doubt as to whether everything is working as intended there - might it hint at rare anon ptes which rmap cannot find? A question not easily answered: put in the fix for missed memcg charges. Cc; Matthew Wilcox Fixes: 4c6355b25e8b ("mm: memcontrol: charge swapin pages on instantiation") Signed-off-by: Hugh Dickins Signed-off-by: Andrew Morton Reviewed-by: Shakeel Butt Acked-by: Johannes Weiner Cc: Alex Shi Cc: Michal Hocko Cc: Mike Kravetz Cc: Qian Cai Cc: [5.8] Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008301343270.5954@eggly.anvils Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008301358020.5954@eggly.anvils Signed-off-by: Linus Torvalds --- mm/ksm.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/ksm.c b/mm/ksm.c index 235f55d01541..9afccc36dbd2 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -2586,6 +2586,10 @@ struct page *ksm_might_need_to_copy(struct page *page, return page; /* let do_swap_page report the error */ new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address); + if (new_page && mem_cgroup_charge(new_page, vma->vm_mm, GFP_KERNEL)) { + put_page(new_page); + new_page = NULL; + } if (new_page) { copy_user_highpage(new_page, page, address, vma);