From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751705AbdB0Qnn (ORCPT ); Mon, 27 Feb 2017 11:43:43 -0500 Received: from mx2.suse.de ([195.135.220.15]:54271 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751486AbdB0Qnm (ORCPT ); Mon, 27 Feb 2017 11:43:42 -0500 Date: Mon, 27 Feb 2017 17:28:03 +0100 From: Michal Hocko To: Shaohua Li Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Kernel-team@fb.com, minchan@kernel.org, hughd@google.com, hannes@cmpxchg.org, riel@redhat.com, mgorman@techsingularity.net, akpm@linux-foundation.org Subject: Re: [PATCH V5 2/6] mm: don't assume anonymous pages have SwapBacked flag Message-ID: <20170227162803.GL26504@dhcp22.suse.cz> References: <3945232c0df3dd6c4ef001976f35a95f18dcb407.1487965799.git.shli@fb.com> <20170227143534.GE26504@dhcp22.suse.cz> <20170227161022.GA62304@shli-mbp.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170227161022.GA62304@shli-mbp.local> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 27-02-17 08:10:24, Shaohua Li wrote: > On Mon, Feb 27, 2017 at 03:35:34PM +0100, Michal Hocko wrote: > > On Fri 24-02-17 13:31:45, Shaohua Li wrote: > > > There are a few places the code assumes anonymous pages should have > > > SwapBacked flag set. MADV_FREE pages are anonymous pages but we are > > > going to add them to LRU_INACTIVE_FILE list and clear SwapBacked flag > > > for them. The assumption doesn't hold any more, so fix them. > > > > > > Cc: Michal Hocko > > > Cc: Minchan Kim > > > Cc: Hugh Dickins > > > Cc: Rik van Riel > > > Cc: Mel Gorman > > > Cc: Andrew Morton > > > Acked-by: Johannes Weiner > > > Signed-off-by: Shaohua Li Anyway, feel free to add Acked-by: Michal Hocko > > > > Looks good to me. > > [...] > > > index 96eb85c..c621088 100644 > > > --- a/mm/rmap.c > > > +++ b/mm/rmap.c > > > @@ -1416,7 +1416,8 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, > > > * Store the swap location in the pte. > > > * See handle_pte_fault() ... > > > */ > > > - VM_BUG_ON_PAGE(!PageSwapCache(page), page); > > > + VM_BUG_ON_PAGE(!PageSwapCache(page) && PageSwapBacked(page), > > > + page); > > > > just this part makes me scratch my head. I really do not understand what > > kind of problem it tries to prevent from, maybe I am missing something > > obvoious... > > Just check a page which isn't lazyfree but wrongly enters here without swap > entry. Or maybe you suggest we delete this statement? Ohh, I figured out when seeing later patch in the series, I then wanted to get back to this one but forgot... This on its own didn't really tell me much. Maybe a comment would be helpful or even drop the VM_BUG_ON altogether. -- Michal Hocko SUSE Labs