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From: Pavel Begunkov <[email protected]>
To: Dave Chinner <[email protected]>
Cc: [email protected], Jens Axboe <[email protected]>,
	Christoph Hellwig <[email protected]>,
	Matthew Wilcox <[email protected]>,
	Ming Lei <[email protected]>,
	Johannes Weiner <[email protected]>,
	Alexander Viro <[email protected]>,
	"Darrick J . Wong" <[email protected]>,
	"Martin K . Petersen" <[email protected]>,
	Jonathan Corbet <[email protected]>,
	[email protected], [email protected],
	[email protected], [email protected],
	[email protected], [email protected],
	[email protected]
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: <[email protected]> (raw)
In-Reply-To: <[email protected]>

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 <[email protected]>
>> Signed-off-by: Pavel Begunkov <[email protected]>
>> ---
>>  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

  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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