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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <163584174921.4023316.8927114426959755223.stgit@warthog.procyon.org.uk> <163584187452.4023316.500389675405550116.stgit@warthog.procyon.org.uk> <1038257.1635951492@warthog.procyon.org.uk> To: Matthew Wilcox Cc: dhowells@redhat.com, Jeff Layton , Marc Dionne , Ilya Dryomov , Dominique Martinet , v9fs-developer@lists.sourceforge.net, linux-afs@lists.infradead.org, ceph-devel@vger.kernel.org, linux-cachefs@redhat.com, linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, devel@lists.orangefs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 5/6] netfs, 9p, afs, ceph: Use folios MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <1760414.1636036338.1@warthog.procyon.org.uk> Content-Transfer-Encoding: quoted-printable Date: Thu, 04 Nov 2021 14:32:18 +0000 Message-ID: <1760415.1636036338@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 48FE5190B X-Stat-Signature: axr9ju3rjz9csnjiy3rp7hn7cf3xfq95 Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=HhWKadzg; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf22.hostedemail.com: domain of dhowells@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=dhowells@redhat.com X-HE-Tag: 1636036361-586500 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: Matthew Wilcox wrote: > On Wed, Nov 03, 2021 at 02:58:12PM +0000, David Howells wrote: > > Matthew Wilcox wrote: > > = > > > > + len =3D (size >=3D start + gran) ? gran : size - start; > > > = > > > This seems like the most complicated way to write this ... how about= : > > > = > > > size_t len =3D min_t(loff_t, isize - start, folio_size(folio= )); > > = > > I was trying to hedge against isize-start going negative. Can this co= de race > > against truncate? truncate_setsize() changes i_size *before* invalida= ting the > > pages. > = > We should check for isize < start separately, and skip the writeback > entirely. So, something like the following static int v9fs_vfs_write_folio_locked(struct folio *folio) { struct inode *inode =3D folio_inode(folio); struct v9fs_inode *v9inode =3D V9FS_I(inode); loff_t start =3D folio_pos(folio); loff_t i_size =3D i_size_read(inode); struct iov_iter from; size_t len =3D folio_size(folio); int err; if (start >=3D i_size) return 0; /* Simultaneous truncation occurred */ len =3D min_t(loff_t, i_size - start, len); iov_iter_xarray(&from, ..., start, len); ... } David