From: Michal Hocko <mhocko@kernel.org>
To: Shaohua Li <shli@kernel.org>
Cc: linux-mm@kvack.org, Artem Savkov <asavkov@redhat.com>,
Kernel-team@fb.com, Shaohua Li <shli@fb.com>,
stable@vger.kernel.org, Johannes Weiner <hannes@cmpxchg.org>,
Hillf Danton <hillf.zj@alibaba-inc.com>,
Minchan Kim <minchan@kernel.org>, Hugh Dickins <hughd@google.com>,
Mel Gorman <mgorman@techsingularity.net>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH V2 1/2] mm: avoid marking swap cached page as lazyfree
Date: Wed, 27 Sep 2017 09:16:09 +0200 [thread overview]
Message-ID: <20170927071609.vywaxvf4gsn2pcvn@dhcp22.suse.cz> (raw)
In-Reply-To: <20170926130705.wjtw55kj7cw4k34j@dhcp22.suse.cz>
[ups this got stuck in the outgoing queue]
On Tue 26-09-17 15:07:05, Michal Hocko wrote:
> On Fri 22-09-17 11:46:30, Shaohua Li wrote:
> > From: Shaohua Li <shli@fb.com>
> >
> > MADV_FREE clears pte dirty bit and then marks the page lazyfree (clear
> > SwapBacked). There is no lock to prevent the page is added to swap cache
> > between these two steps by page reclaim. If the page is added to swap
> > cache, marking the page lazyfree will confuse page fault if the page is
> > reclaimed and refault.
>
> Could you be more specific how exactly what kind of the confusion is the
> result? I suspect you are talking about VM_BUG_ON_PAGE in
> __add_to_swap_cache right?
I completely mixed reclaim and the #PF path here
> I am also not sure how that would actually happen to be honest. If we
> raced with the reclaim then the page should have been isolated and so
> PageLRU is no longer true. Or am I missing something?
And here I've completely missed that the swapcache page will go back to
the LRU. Stupid me. Your new changelog [1] explained it all. Thanks and
sorry for these stupid questions.
[1] http://lkml.kernel.org/r/6537ef3814398c0073630b03f176263bc81f0902.1506446061.git.shli@fb.com
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2017-09-27 7:16 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-22 18:46 [PATCH V2 0/2] mm: fix race condition in MADV_FREE Shaohua Li
2017-09-22 18:46 ` [PATCH V2 1/2] mm: avoid marking swap cached page as lazyfree Shaohua Li
2017-09-25 5:07 ` Minchan Kim
2017-09-26 13:07 ` Michal Hocko
2017-09-27 7:16 ` Michal Hocko [this message]
2017-09-22 18:46 ` [PATCH V2 2/2] mm: fix data corruption caused by lazyfree page Shaohua Li
2017-09-26 13:13 ` Michal Hocko
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