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Carvalho" Date: Mon, 24 Feb 2025 12:50:48 -0300 X-Gm-Features: AWEUYZmCaVei4AAfqe3vnNodRbnQHoRP0SLFpgUKuQd_na8KPtvHoJlGT8fEx1Y Message-ID: Subject: Re: [PATCH v2] mm: Fix error handling in __filemap_get_folio() with FGP_NOWAIT To: Matthew Wilcox Cc: Christoph Hellwig , linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, djwong@kernel.org, Dave Chinner Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-CLOUD-SEC-AV-Sent: true X-CLOUD-SEC-AV-Info: scylladb,google_mail,monitor X-Gm-Spam: 0 X-Gm-Phishy: 0 X-CLOUD-SEC-AV-Sent: true X-CLOUD-SEC-AV-Info: scylla,google_mail,monitor X-Gm-Spam: 0 X-Gm-Phishy: 0 X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 99B2AC0013 X-Stat-Signature: mncueqmtumryn8sj54gyzwhbc9bewcck X-HE-Tag: 1740412265-194283 X-HE-Meta: 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 jflulCKl AHnedG0D39N7EnNJvC/qaf/AxqGRzpQHHCB2Us6RdsH6EDRrSSPuuEuXqfgqCocC7beBhJjyjTOXLwJdbbNrJFYEhQSh2fjSLQPyOVMipc57miS0ZM7c5Yik6nLcNSl5c/PpMyNyyZoXIKkE5NNxrJTXy6jUCt1f8Jz8mbwVTMwdKMAiKeFu/u8YtkGO6xZPku4vFxrhfPsSmZRv8W9kxWIFhr81eAXmpLT3xMEqf4zubvhV4MjzJdlg/sQV4FQLJC8adFqpHQYcbu9uh5GnQj59pUdH0jQbOeiurU536wFdfVFIm1SQ6r8byvA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.001741, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Feb 24, 2025 at 12:49=E2=80=AFPM Matthew Wilcox wrote: > > On Mon, Feb 24, 2025 at 12:45:21PM -0300, Raphael S. Carvalho wrote: > > On Mon, Feb 24, 2025 at 12:33=E2=80=AFPM Matthew Wilcox wrote: > > > > > > On Mon, Feb 24, 2025 at 03:17:44PM +0100, Christoph Hellwig wrote: > > > > On Mon, Feb 24, 2025 at 05:13:28AM -0300, Raphael S. Carvalho wrote= : > > > > > + if (err) { > > > > > + /* Prevents -ENOMEM from escaping to user spa= ce with FGP_NOWAIT */ > > > > > + if ((fgp_flags & FGP_NOWAIT) && err =3D=3D -E= NOMEM) > > > > > + err =3D -EAGAIN; > > > > > return ERR_PTR(err); > > > > > > > > I don't think the comment is all that useful. It's also overly lon= g. > > > > > > > > I'd suggest this instead: > > > > > > > > /* > > > > * When NOWAIT I/O fails to allocate folios t= his could > > > > * be due to a nonblocking memory allocation = and not > > > > * because the system actually is out of memo= ry. > > > > * Return -EAGAIN so that there caller retrie= s in a > > > > * blocking fashion instead of propagating -E= NOMEM > > > > * to the application. > > > > */ > > > > > > I don't think it needs a comment at all, but the memory allocation > > > might be for something other than folios, so your suggested comment > > > is misleading. > > > > Isn't it all in the context of allocating or adding folio? The reason > > behind a comment is to prevent movements in the future that could > > cause a similar regression, and also to inform the poor reader that > > might be left wondering why we're converting -ENOMEM into -EAGAIN with > > FGP_NOWAIT. Can it be slightly adjusted to make it more correct? Or > > you really think it's better to remove it completely? > > I really don't think the comment is needed. This is a common mistake > when fixing a bug. Ok, so I will proceed with v4 now, removing the comment.