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Tue, 12 Nov 2024 11:36:14 -0500 X-MC-Unique: 2e90iJDzPXGIadG2_ei9PQ-1 X-Mimecast-MFC-AGG-ID: 2e90iJDzPXGIadG2_ei9PQ Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E7CEF19560B8; Tue, 12 Nov 2024 16:36:12 +0000 (UTC) Received: from bfoster (unknown [10.22.80.120]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id CFDC819560A3; Tue, 12 Nov 2024 16:36:10 +0000 (UTC) Date: Tue, 12 Nov 2024 11:37:43 -0500 From: Brian Foster To: Jens Axboe Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, hannes@cmpxchg.org, clm@meta.com, linux-kernel@vger.kernel.org, willy@infradead.org, kirill@shutemov.name, linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org Subject: Re: [PATCH 13/16] iomap: make buffered writes work with RWF_UNCACHED Message-ID: References: <20241111234842.2024180-1-axboe@kernel.dk> <20241111234842.2024180-14-axboe@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241111234842.2024180-14-axboe@kernel.dk> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 91DA32000F X-Stat-Signature: rzseciy6afkxbhht8xyjzf7bms48h3h7 X-HE-Tag: 1731429359-834731 X-HE-Meta: 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 WR/mymYV t2Cm/WA5IBms9saCSvg1dlLUDG/Ndvcy/dpgP+D6q5F+unNPuTJI766VAvpzDj0dChSVSKFuydAN56Q+JLcDJKJW0jBNrhakUP3qUO5pQv3v61OhrTHti38ThWal7zqQwGgdRxtQMoiE6XEjbUD16ZK+pM2Y1RXA67oYCXU1NnK3lzTfSMbJypdg2aNb2HzKea5sUenstgeNeLF1sLAZZ8n5rYMRd+Nl2vXWVqtAH8Blxct8h2KQNSFiWsUy1Fzl0T0djCBz4PXRfzSAQTgyAwXyDGILxboCr49re2kfqSPk/TFuH1Sb/8N3UDmSKI/NzN+c3adXc3nDBiBMU2v/da6SLi9QE/mZSZeqosf0ks7yFG66w93+K0VJ+ANySaOEI45vuzwSOUnFuKMA9F4+gmDSnTw== 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: List-Subscribe: List-Unsubscribe: On Mon, Nov 11, 2024 at 04:37:40PM -0700, Jens Axboe wrote: > Add iomap buffered write support for RWF_UNCACHED. If RWF_UNCACHED is > set for a write, mark the folios being written with drop_writeback. Then s/drop_writeback/uncached/ ? BTW, this might be getting into wonky "don't care that much" territory, but something else to be aware of is that certain writes can potentially change pagecache state as a side effect outside of the actual buffered write itself. For example, xfs calls iomap_zero_range() on write extension (i.e. pos > isize), which uses buffered writes and thus could populate a pagecache folio without setting it uncached, even if done on behalf of an uncached write. I've only made a first pass and could be missing some details, but IIUC I _think_ this means something like writing out a stream of small, sparse and file extending uncached writes could actually end up behaving more like sync I/O. Again, not saying that's something we really care about, just raising it in case it's worth considering or documenting.. Brian > writeback completion will drop the pages. The write_iter handler simply > kicks off writeback for the pages, and writeback completion will take > care of the rest. > > This still needs the user of the iomap buffered write helpers to call > iocb_uncached_write() upon successful issue of the writes. > > Signed-off-by: Jens Axboe > --- > fs/iomap/buffered-io.c | 15 +++++++++++++-- > include/linux/iomap.h | 4 +++- > 2 files changed, 16 insertions(+), 3 deletions(-) > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > index ef0b68bccbb6..2f2a5db04a68 100644 > --- a/fs/iomap/buffered-io.c > +++ b/fs/iomap/buffered-io.c > @@ -603,6 +603,8 @@ struct folio *iomap_get_folio(struct iomap_iter *iter, loff_t pos, size_t len) > > if (iter->flags & IOMAP_NOWAIT) > fgp |= FGP_NOWAIT; > + if (iter->flags & IOMAP_UNCACHED) > + fgp |= FGP_UNCACHED; > fgp |= fgf_set_order(len); > > return __filemap_get_folio(iter->inode->i_mapping, pos >> PAGE_SHIFT, > @@ -1023,8 +1025,9 @@ ssize_t > iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *i, > const struct iomap_ops *ops, void *private) > { > + struct address_space *mapping = iocb->ki_filp->f_mapping; > struct iomap_iter iter = { > - .inode = iocb->ki_filp->f_mapping->host, > + .inode = mapping->host, > .pos = iocb->ki_pos, > .len = iov_iter_count(i), > .flags = IOMAP_WRITE, > @@ -1034,9 +1037,14 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *i, > > if (iocb->ki_flags & IOCB_NOWAIT) > iter.flags |= IOMAP_NOWAIT; > + if (iocb->ki_flags & IOCB_UNCACHED) > + iter.flags |= IOMAP_UNCACHED; > > - while ((ret = iomap_iter(&iter, ops)) > 0) > + while ((ret = iomap_iter(&iter, ops)) > 0) { > + if (iocb->ki_flags & IOCB_UNCACHED) > + iter.iomap.flags |= IOMAP_F_UNCACHED; > iter.processed = iomap_write_iter(&iter, i); > + } > > if (unlikely(iter.pos == iocb->ki_pos)) > return ret; > @@ -1770,6 +1778,9 @@ static int iomap_add_to_ioend(struct iomap_writepage_ctx *wpc, > size_t poff = offset_in_folio(folio, pos); > int error; > > + if (folio_test_uncached(folio)) > + wpc->iomap.flags |= IOMAP_F_UNCACHED; > + > if (!wpc->ioend || !iomap_can_add_to_ioend(wpc, pos)) { > new_ioend: > error = iomap_submit_ioend(wpc, 0); > diff --git a/include/linux/iomap.h b/include/linux/iomap.h > index f61407e3b121..2efc72df19a2 100644 > --- a/include/linux/iomap.h > +++ b/include/linux/iomap.h > @@ -64,6 +64,7 @@ struct vm_fault; > #define IOMAP_F_BUFFER_HEAD 0 > #endif /* CONFIG_BUFFER_HEAD */ > #define IOMAP_F_XATTR (1U << 5) > +#define IOMAP_F_UNCACHED (1U << 6) > > /* > * Flags set by the core iomap code during operations: > @@ -173,8 +174,9 @@ struct iomap_folio_ops { > #define IOMAP_NOWAIT (1 << 5) /* do not block */ > #define IOMAP_OVERWRITE_ONLY (1 << 6) /* only pure overwrites allowed */ > #define IOMAP_UNSHARE (1 << 7) /* unshare_file_range */ > +#define IOMAP_UNCACHED (1 << 8) /* uncached IO */ > #ifdef CONFIG_FS_DAX > -#define IOMAP_DAX (1 << 8) /* DAX mapping */ > +#define IOMAP_DAX (1 << 9) /* DAX mapping */ > #else > #define IOMAP_DAX 0 > #endif /* CONFIG_FS_DAX */ > -- > 2.45.2 > >