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Wed, 19 Aug 2020 13:15:21 -0700 (PDT) Received: from xiangao.remote.csb ([209.132.188.80]) by smtp.gmail.com with ESMTPSA id s125sm56651pfc.63.2020.08.19.13.15.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 Aug 2020 13:15:20 -0700 (PDT) Date: Thu, 20 Aug 2020 04:15:09 +0800 From: Gao Xiang To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Rafael Aquini , Carlos Maiolino , Eric Sandeen , "Huang, Ying" , stable Subject: Re: [PATCH] mm, THP, swap: fix allocating cluster for swapfile by mistake Message-ID: <20200819201509.GA26216@xiangao.remote.csb> References: <20200819195613.24269-1-hsiangkao@redhat.com> <20200819130506.eea076dd618644cd7ff875b6@linux-foundation.org> MIME-Version: 1.0 In-Reply-To: <20200819130506.eea076dd618644cd7ff875b6@linux-foundation.org> User-Agent: Mutt/1.10.1 (2018-07-13) Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=hsiangkao@redhat.com X-Mimecast-Spam-Score: 0.003 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspamd-Queue-Id: D350C180D0181 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hi Andrew, On Wed, Aug 19, 2020 at 01:05:06PM -0700, Andrew Morton wrote: > On Thu, 20 Aug 2020 03:56:13 +0800 Gao Xiang wrote: > > > SWP_FS doesn't mean the device is file-backed swap device, > > which just means each writeback request should go through fs > > by DIO. Or it'll just use extents added by .swap_activate(), > > but it also works as file-backed swap device. > > This is very hard to understand :( Thanks for your reply... The related logic is in __swap_writepage() and setup_swap_extents(), and also see e.g generic_swapfile_activate() or iomap_swapfile_activate()... I will also talk with "Huang, Ying" in person if no response here. > > > So in order to achieve the goal of the original patch, > > SWP_BLKDEV should be used instead. > > > > FS corruption can be observed with SSD device + XFS + > > fragmented swapfile due to CONFIG_THP_SWAP=y. > > > > Fixes: f0eea189e8e9 ("mm, THP, swap: Don't allocate huge cluster for file backed swap device") > > Fixes: 38d8b4e6bdc8 ("mm, THP, swap: delay splitting THP during swap out") > > Why do you think it has taken three years to discover this? I'm not sure if the Redhat BZ is available for public, it can be reproduced since rhel 8 https://bugzilla.redhat.com/show_bug.cgi?id=1855474 It seems hard to believe, but I think just because rare user uses the SSD device + THP + file-backed swap device combination... maybe I'm wrong here, but my test shows as it is. Thanks, Gao Xiang > > >