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From: Johannes Weiner <hannes@cmpxchg.org>
To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Alex Shi <alex.shi@linux.alibaba.com>,
	Michal Hocko <mhocko@suse.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Shakeel Butt <shakeelb@google.com>,
	Matthew Wilcox <willy@infradead.org>, Qian Cai <cai@lca.pw>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 1/5] ksm: reinstate memcg charge on copied pages
Date: Tue, 1 Sep 2020 11:01:49 -0400	[thread overview]
Message-ID: <20200901150149.GA45118@cmpxchg.org> (raw)
In-Reply-To: <alpine.LSU.2.11.2008301358020.5954@eggly.anvils>

On Sun, Aug 30, 2020 at 01:59:35PM -0700, Hugh Dickins wrote:
> 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.
> 
> Fixes: 4c6355b25e8b ("mm: memcontrol: charge swapin pages on instantiation")
> Signed-off-by: Hugh Dickins <hughd@google.com>
> Cc: stable@vger.kernel.org # v5.8

Acked-by: Johannes Weiner <hannes@cmpxchg.org>


  parent reply	other threads:[~2020-09-01 15:04 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-30 20:57 [PATCH 0/5] mm: fixes to past from future testing Hugh Dickins
2020-08-30 20:59 ` [PATCH 1/5] ksm: reinstate memcg charge on copied pages Hugh Dickins
2020-08-31 14:40   ` Shakeel Butt
2020-09-01 15:01   ` Johannes Weiner [this message]
2020-08-30 21:01 ` [PATCH 2/5] mm: migration of hugetlbfs page skip memcg Hugh Dickins
2020-08-31 14:40   ` Shakeel Butt
2020-09-01 15:02   ` Johannes Weiner
2020-08-30 21:08 ` [PATCH 4/5] mm: fix check_move_unevictable_pages() on THP Hugh Dickins
2020-08-31 14:44   ` Shakeel Butt
2020-09-01  2:04   ` Alex Shi
2020-09-01  3:59     ` Hugh Dickins
2020-09-01 15:57   ` Yang Shi
2020-08-30 21:09 ` [PATCH 5/5] mlock: fix unevictable_pgs event counts " Hugh Dickins
2020-08-31 14:45   ` Shakeel Butt
2020-09-01 15:41   ` Yang Shi
2020-09-01  2:28 ` [PATCH 0/5] mm: fixes to past from future testing Alex Shi
2020-09-01  4:08   ` Hugh Dickins

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