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Sat, 2 May 2020 15:53:54 -0400 (EDT) Received: from vostro.rath.org (vostro [192.168.12.4]) by ebox.rath.org (Postfix) with ESMTPS id 556A523; Sat, 2 May 2020 19:53:53 +0000 (UTC) Received: by vostro.rath.org (Postfix, from userid 1000) id 2E36EE29E2; Sat, 2 May 2020 20:52:48 +0100 (BST) From: Nikolaus Rath To: linux-fsdevel@vger.kernel.org Cc: fuse-devel , linux-mm , miklos , Gabriel Krisman Bertazi , =?utf-8?Q?Andr=C3=A9?= Almeida Subject: Re: fuse: trying to steal weird page References: <87a72qtaqk.fsf@vostro.rath.org> Mail-Copies-To: never Mail-Followup-To: linux-fsdevel@vger.kernel.org, fuse-devel , linux-mm , miklos , Gabriel Krisman Bertazi , =?utf-8?Q?Andr=C3=A9?= Almeida Date: Sat, 02 May 2020 20:52:48 +0100 In-Reply-To: <87a72qtaqk.fsf@vostro.rath.org> (Nikolaus Rath's message of "Sat, 02 May 2020 20:09:23 +0100") Message-ID: <877dxut8q7.fsf@vostro.rath.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable 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 May 02 2020, Nikolaus Rath wrote: > Hello, > > I have recently noticed that a FUSE filesystem regularly produces many > kernel messages like this: > > [ 2333.009931] fuse: trying to steal weird page > [ 2333.009937] fuse: page=3D00000000dd1750e3 index=3D2022240 flags=3D17ff= ffc0000097, count=3D1, > mapcount=3D0, mapping=3D00000000125079ad > [ 2334.595835] fuse: trying to steal weird page > [ 2334.595841] fuse: page=3D000000009e8626ac index=3D2052288 flags=3D17ff= ffc0000097, count=3D1, > mapcount=3D0, mapping=3D00000000125079ad > [ 2334.983568] fuse: trying to steal weird page > [ 2334.983572] fuse: page=3D0000000013fdd9e4 index=3D2059392 flags=3D17ff= ffc0000097, count=3D1, > mapcount=3D0, mapping=3D00000000125079ad > [ 2335.979905] fuse: trying to steal weird page > [ 2335.979911] fuse: page=3D00000000a7057848 index=3D2078588 flags=3D17ff= ffc0000097, count=3D1, > mapcount=3D0, mapping=3D00000000125079ad > > They do not seem to correlate with userspace errors, but I noticed that > there is no significant performance difference between libfuse using > splice, splice with SPLICE_MOVE, and not using splice. This is somewhat > unexpected, so maybe it is related to the kernel messages? > > What are the implications of the above kernel message? Is there a way to > provide more debugging information? > > (I have reported a similar issue before > (https://marc.info/?l=3Dlinux-mm&m=3D155290847909996&w=3D2) and the patch= may > not be present in the kernel that I'm using. However, the previous time > the warning had a different set of flags and a null mapping, so I think > this one is different). > > $ uname -a > Linux valve 5.3.0-46-generic #38-Ubuntu SMP Fri Mar 27 17:37:05 UTC 2020 = x86_64 x86_64 x86_64 GNU/Linux I have now reproduced this with a vanilla 5.6 kernel. I also found that the "mapping" and "flags" parameters always have the same values - even across different workloads and when re-mounting the filesystem. The "page" parameter varies. Best, -Nikolaus --=20 GPG Fingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F =C2=BBTime flies like an arrow, fruit flies like a Banana.=C2= =AB