From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 26 Sep 2017 15:25:24 -0400 From: Johannes Weiner To: Shaohua Li Cc: linux-mm@kvack.org, asavkov@redhat.com, Kernel-team@fb.com, Shaohua Li , stable@vger.kernel.org, Michal Hocko , Hillf Danton , Minchan Kim , Hugh Dickins , Mel Gorman , Andrew Morton Subject: Re: [PATCH V3 1/2] mm: avoid marking swap cached page as lazyfree Message-ID: <20170926192524.GA30943@cmpxchg.org> References: <6537ef3814398c0073630b03f176263bc81f0902.1506446061.git.shli@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6537ef3814398c0073630b03f176263bc81f0902.1506446061.git.shli@fb.com> Sender: owner-linux-mm@kvack.org List-ID: On Tue, Sep 26, 2017 at 10:26:25AM -0700, Shaohua Li wrote: > From: Shaohua Li > > 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. The patch lgtm, but for the changelog it probably makes sense to start with the user-visible behavior, i.e. the endlessly looping swap fault handler because it thinks it's racing with the swap slot being freed. Makes it easier for other distro/vendor people to identify this for backporting. On that note, I think this should go into 4.13 and be tagged for 4.12 stable. > Reported-and-tested-by: Artem Savkov > Fix: 802a3a92ad7a(mm: reclaim MADV_FREE pages) > Signed-off-by: Shaohua Li > Cc: stable@vger.kernel.org > Cc: Johannes Weiner > Cc: Michal Hocko > Cc: Hillf Danton > Cc: Minchan Kim > Cc: Hugh Dickins > Cc: Mel Gorman > Cc: Andrew Morton > Reviewed-by: Rik van Riel Acked-by: Johannes Weiner -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org