From: Pavel Begunkov <asml.silence@gmail.com>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-block@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
Christoph Hellwig <hch@infradead.org>,
Matthew Wilcox <willy@infradead.org>,
Ming Lei <ming.lei@redhat.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
"Darrick J . Wong" <darrick.wong@oracle.com>,
"Martin K . Petersen" <martin.petersen@oracle.com>,
Jonathan Corbet <corbet@lwn.net>,
linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
io-uring@vger.kernel.org, linux-kernel@vger.kernel.org,
target-devel@vger.kernel.org, linux-scsi@vger.kernel.org,
linux-doc@vger.kernel.org
Subject: Re: [PATCH v1 6/6] block/iomap: don't copy bvec for direct IO
Date: Tue, 15 Dec 2020 01:15:37 +0000 [thread overview]
Message-ID: <d2689b7c-7200-24cc-761c-bcbaa21c40ae@gmail.com> (raw)
In-Reply-To: <20201215010921.GH632069@dread.disaster.area>
On 15/12/2020 01:09, Dave Chinner wrote:
> On Tue, Dec 15, 2020 at 12:20:25AM +0000, Pavel Begunkov wrote:
>> The block layer spends quite a while in blkdev_direct_IO() to copy and
>> initialise bio's bvec. However, if we've already got a bvec in the input
>> iterator it might be reused in some cases, i.e. when new
>> ITER_BVEC_FLAG_FIXED flag is set. Simple tests show considerable
>> performance boost, and it also reduces memory footprint.
>>
>> Suggested-by: Matthew Wilcox <willy@infradead.org>
>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
>> ---
>> Documentation/filesystems/porting.rst | 9 ++++
>> block/bio.c | 64 +++++++++++----------------
>> include/linux/bio.h | 3 ++
>> 3 files changed, 38 insertions(+), 38 deletions(-)
>
> This doesn't touch iomap code, so the title of the patch seems
> wrong...
yeah, should be bio.
>
>> +For bvec based itererators bio_iov_iter_get_pages() now doesn't copy bvecs but
>> +uses the one provided. Anyone issuing kiocb-I/O should ensure that the bvec and
>> +page references stay until I/O has completed, i.e. until ->ki_complete() has
>> +been called or returned with non -EIOCBQUEUED code.
>
> This is hard to follow. Perhaps:
>
> bio_iov_iter_get_pages() uses the bvecs provided for bvec based
> iterators rather than copying them. Hence anyone issuing kiocb based
> IO needs to ensure the bvecs and pages stay referenced until the
> submitted I/O is completed by a call to ->ki_complete() or returns
> with an error other than -EIOCBQUEUED.
Agree, that's easier to read, thanks
>
>> diff --git a/include/linux/bio.h b/include/linux/bio.h
>> index 2a9f3f0bbe0a..337f4280b639 100644
>> --- a/include/linux/bio.h
>> +++ b/include/linux/bio.h
>> @@ -444,6 +444,9 @@ static inline void bio_wouldblock_error(struct bio *bio)
>>
>> static inline int bio_iov_vecs_to_alloc(struct iov_iter *iter, int max_segs)
>> {
>> + /* reuse iter->bvec */
>> + if (iov_iter_is_bvec(iter))
>> + return 0;
>> return iov_iter_npages(iter, max_segs);
>
> Ah, I'm a blind idiot... :/
>
> Cheers,
>
> Dave.
>
--
Pavel Begunkov
next prev parent reply other threads:[~2020-12-15 1:19 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-15 0:20 [PATCH v1 0/6] no-copy bvec Pavel Begunkov
2020-12-15 0:20 ` [PATCH v1 1/6] target/file: allocate the bvec array as part of struct target_core_file_cmd Pavel Begunkov
2020-12-15 0:20 ` [PATCH v1 2/6] iov_iter: optimise bvec iov_iter_advance() Pavel Begunkov
2020-12-15 9:37 ` David Laight
2020-12-15 11:23 ` Pavel Begunkov
2020-12-15 13:54 ` David Laight
2020-12-15 13:56 ` Pavel Begunkov
2020-12-22 14:03 ` Christoph Hellwig
2020-12-15 0:20 ` [PATCH v1 3/6] bio: deduplicate adding a page into bio Pavel Begunkov
2020-12-22 14:04 ` Christoph Hellwig
2020-12-15 0:20 ` [PATCH v1 4/6] block/psi: remove PSI annotations from direct IO Pavel Begunkov
2020-12-15 0:56 ` Dave Chinner
2020-12-15 1:03 ` Pavel Begunkov
2020-12-15 1:33 ` Dave Chinner
2020-12-15 11:41 ` Pavel Begunkov
2020-12-22 14:07 ` Christoph Hellwig
2020-12-15 0:20 ` [PATCH v1 5/6] bio: add a helper calculating nr segments to alloc Pavel Begunkov
2020-12-15 1:00 ` Dave Chinner
2020-12-15 1:07 ` Pavel Begunkov
2020-12-15 1:09 ` Dave Chinner
2020-12-22 14:07 ` Christoph Hellwig
2020-12-15 0:20 ` [PATCH v1 6/6] block/iomap: don't copy bvec for direct IO Pavel Begunkov
2020-12-15 1:09 ` Dave Chinner
2020-12-15 1:15 ` Pavel Begunkov [this message]
2020-12-22 14:15 ` Christoph Hellwig
2020-12-15 1:41 ` [PATCH v1 0/6] no-copy bvec Ming Lei
2020-12-15 11:14 ` Pavel Begunkov
2020-12-15 12:03 ` Ming Lei
2020-12-15 14:05 ` Pavel Begunkov
2020-12-22 14:11 ` Christoph Hellwig
2020-12-23 12:52 ` Pavel Begunkov
2020-12-23 15:51 ` Christoph Hellwig
2020-12-23 16:04 ` James Bottomley
2020-12-23 20:23 ` Douglas Gilbert
2020-12-23 20:32 ` Pavel Begunkov
2020-12-24 6:41 ` Christoph Hellwig
2020-12-24 16:45 ` Douglas Gilbert
2020-12-24 17:30 ` James Bottomley
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