From: Minchan Kim <minchan@kernel.org>
To: Shaohua Li <shli@kernel.org>
Cc: linux-mm@kvack.org, asavkov@redhat.com, Kernel-team@fb.com,
Shaohua Li <shli@fb.com>,
stable@vger.kernel.org, Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@suse.com>,
Hillf Danton <hillf.zj@alibaba-inc.com>,
Hugh Dickins <hughd@google.com>,
Mel Gorman <mgorman@techsingularity.net>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH V3 1/2] mm: avoid marking swap cached page as lazyfree
Date: Wed, 27 Sep 2017 08:20:05 +0900 [thread overview]
Message-ID: <20170926232005.GA32370@bbox> (raw)
In-Reply-To: <6537ef3814398c0073630b03f176263bc81f0902.1506446061.git.shli@fb.com>
On Tue, Sep 26, 2017 at 10:26:25AM -0700, 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. Page reclaim could add the page
> to swap cache and unmap the page. After page reclaim, the page is added
> back to lru. At that time, we probably start draining per-cpu pagevec
> and mark the page lazyfree. So the page could be in a state with
> SwapBacked cleared and PG_swapcache set. Next time there is a refault in
> the virtual address, do_swap_page can find the page from swap cache but
> the page has PageSwapCache false because SwapBacked isn't set, so
> do_swap_page will bail out and do nothing. The task will keep running
> into fault handler.
With new description, I got why you want to seperate this. Yub, it should
be separated. Sorry for the noise. What I was missing is PageSwapCache's
change which checked PG_swapbacked as well as PG_swapcache. I didn't
notice that the change.
Acked-by: Minchan Kim <minchan@kernel.org>
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next prev parent reply other threads:[~2017-09-26 23:20 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-26 17:26 [PATCH V3 0/2] mm: fix race condition in MADV_FREE Shaohua Li
2017-09-26 17:26 ` [PATCH V3 1/2] mm: avoid marking swap cached page as lazyfree Shaohua Li
2017-09-26 19:25 ` Johannes Weiner
2017-09-26 20:23 ` Michal Hocko
2017-09-26 23:20 ` Minchan Kim [this message]
2017-09-26 17:26 ` [PATCH V3 2/2] mm: fix data corruption caused by lazyfree page Shaohua Li
2017-09-26 19:40 ` Johannes Weiner
2017-09-26 19:46 ` Shaohua Li
2017-09-26 23:20 ` Minchan Kim
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