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s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=hTEF7FpoeYL8Q+HCa82yrWFkKA4EpFDf03/6zdi5GWQ=; b=TBzHCbSAFIA6DI6KGEAhmbgJvI1TVyX4S+IhDpdlORU6EX8aZoB4g/JpZkvz+2Ej8+ jnZtokVDkDYogr7/3kHE5R9DUTlakx/ccumK/s6jvqo40nur+G4mNzuikqjRAO730cIl QZ7YMP8w1O/7RtLnKlZ0oBSMjoLkCegYM+LwG/+WuFsUD6gMsBAEJ9iKde/3I6nLGdSS e15LvuQv1sdPTaDDOv6d3ZMK1wy5/JiG1rCF3rMbroftlksbvgXxvL0ePgPmbbp3iQWU +ir9X8Q+hR71F8jwZz7Ds7AMnT22jg03Q28b09xFvnPsjLeMyFI7z++HcdxHax7I0eLa TN7w== X-Gm-Message-State: AOAM533LJQryeqjRqqvtEC7WWFGLb6KlMZWOvmauabPKsUHuFLQIt15P m9SrIZuK6bskhznHqhxUOc3xiY8dqakL9k41nKE= X-Google-Smtp-Source: ABdhPJwxPAtVBNKW3xTK2NrvC/hdbP3RA59iQgS6IIjCTV03UOTkvS8epO49JduoeBGiyV5jkb2JDkwmGaRxRFVlIZk= X-Received: by 2002:a17:906:ca4f:: with SMTP id jx15mr302048ejb.449.1597873282341; Wed, 19 Aug 2020 14:41:22 -0700 (PDT) MIME-Version: 1.0 References: <20200819195613.24269-1-hsiangkao@redhat.com> <20200819130506.eea076dd618644cd7ff875b6@linux-foundation.org> <20200819201509.GA26216@xiangao.remote.csb> In-Reply-To: <20200819201509.GA26216@xiangao.remote.csb> From: Yang Shi Date: Wed, 19 Aug 2020 14:41:08 -0700 Message-ID: Subject: Re: [PATCH] mm, THP, swap: fix allocating cluster for swapfile by mistake To: Gao Xiang Cc: Andrew Morton , Linux MM , Linux Kernel Mailing List , Rafael Aquini , Carlos Maiolino , Eric Sandeen , "Huang, Ying" , stable Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 32F791814B0C7 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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: On Wed, Aug 19, 2020 at 1:15 PM Gao Xiang wrote: > > 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 think just NFS falls into this case, so you may rephrase it to: SWP_FS is only used for swap files over NFS. So, !SWP_FS means non NFS swap, it could be either file backed or device backed. Does this look more understandable? > 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 > > > > > > > > >