From: Hugh Dickins hughd@google.com Subject: 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.

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 Fixes: 4c6355b25e8b ("mm: memcontrol: charge swapin pages on instantiation") Signed-off-by: Hugh Dickins hughd@google.com Reviewed-by: Shakeel Butt shakeelb@google.com Acked-by: Johannes Weiner hannes@cmpxchg.org Cc: Alex Shi alex.shi@linux.alibaba.com Cc: Michal Hocko mhocko@suse.com Cc: Mike Kravetz mike.kravetz@oracle.com Cc; Matthew Wilcox willy@infradead.org Cc: Qian Cai cai@lca.pw Cc: stable@vger.kernel.org [5.8] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/ksm.c | 4 ++++ 1 file changed, 4 insertions(+)

--- a/mm/ksm.c~ksm-reinstate-memcg-charge-on-copied-pages +++ a/mm/ksm.c @@ -2586,6 +2586,10 @@ struct page *ksm_might_need_to_copy(stru 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);

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