From: Goldwyn Rodrigues <rgoldwyn@suse.de>
To: "Darrick J. Wong" <darrick.wong@oracle.com>,
Christoph Hellwig <hch@infradead.org>
Cc: linux-fsdevel@vger.kernel.org, jack@suse.com,
linux-block@vger.kernel.org, linux-btrfs@vger.kernel.org,
linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org,
sagi@grimberg.me, avi@scylladb.com, axboe@kernel.dk,
linux-api@vger.kernel.org, willy@infradead.org,
tom.leiming@gmail.com, Goldwyn Rodrigues <rgoldwyn@suse.com>
Subject: Re: [PATCH 7/8] nowait aio: xfs
Date: Fri, 7 Apr 2017 06:34:28 -0500 [thread overview]
Message-ID: <6cc69b0c-7af4-879e-1012-aae8ba5358bd@suse.de> (raw)
In-Reply-To: <20170406225415.GC4864@birch.djwong.org>
On 04/06/2017 05:54 PM, Darrick J. Wong wrote:
> On Mon, Apr 03, 2017 at 11:52:11PM -0700, Christoph Hellwig wrote:
>>> + if (unaligned_io) {
>>> + /* If we are going to wait for other DIO to finish, bail */
>>> + if ((iocb->ki_flags & IOCB_NOWAIT) &&
>>> + atomic_read(&inode->i_dio_count))
>>> + return -EAGAIN;
>>> inode_dio_wait(inode);
>>
>> This checks i_dio_count twice in the nowait case, I think it should be:
>>
>> if (iocb->ki_flags & IOCB_NOWAIT) {
>> if (atomic_read(&inode->i_dio_count))
>> return -EAGAIN;
>> } else {
>> inode_dio_wait(inode);
>> }
>>
>>> if ((flags & (IOMAP_WRITE | IOMAP_ZERO)) && xfs_is_reflink_inode(ip)) {
>>> if (flags & IOMAP_DIRECT) {
>>> + /* A reflinked inode will result in CoW alloc */
>>> + if (flags & IOMAP_NOWAIT) {
>>> + error = -EAGAIN;
>>> + goto out_unlock;
>>> + }
>>
>> This is a bit pessimistic - just because the inode has any shared
>> extents we could still write into unshared ones. For now I think this
>> pessimistic check is fine, but the comment should be corrected.
>
> Consider what happens in both _reflink_{allocate,reserve}_cow. If there
> is already an existing reservation in the CoW fork then we'll have to
> CoW and therefore can't satisfy the NOWAIT flag. If there isn't already
> anything in the CoW fork, then we have to see if there are shared blocks
> by calling _reflink_trim_around_shared. That performs a refcountbt
> lookup, which involves locking the AGF, so we also can't satisfy NOWAIT.
>
> IOWs, I think this hunk has to move outside the IOMAP_DIRECT check to
> cover both write-to-reflinked-file cases.
>
IOMAP_NOWAIT is set only with IOMAP_DIRECT since the nowait feature is
for direct-IO only. This is checked early on, when we are checking for
user-passed flags, and if not, -EINVAL is returned.
--
Goldwyn
next prev parent reply other threads:[~2017-04-07 11:34 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-03 18:52 [PATCH 0/8 v4] No wait AIO Goldwyn Rodrigues
[not found] ` <20170403185307.6243-1-rgoldwyn-l3A5Bk7waGM@public.gmane.org>
2017-04-03 18:53 ` [PATCH 1/8] nowait aio: Introduce IOCB_RW_FLAG_NOWAIT Goldwyn Rodrigues
2017-04-04 6:48 ` Christoph Hellwig
2017-04-03 18:53 ` [PATCH 8/8] nowait aio: btrfs Goldwyn Rodrigues
2017-04-03 18:53 ` [PATCH 2/8] nowait aio: Return if cannot get hold of i_rwsem Goldwyn Rodrigues
2017-04-03 18:53 ` [PATCH 3/8] nowait aio: return if direct write will trigger writeback Goldwyn Rodrigues
2017-04-03 18:53 ` [PATCH 4/8] nowait-aio: Introduce IOMAP_NOWAIT Goldwyn Rodrigues
2017-04-03 18:53 ` [PATCH 5/8] nowait aio: return on congested block device Goldwyn Rodrigues
2017-04-04 6:49 ` Christoph Hellwig
2017-04-03 18:53 ` [PATCH 6/8] nowait aio: ext4 Goldwyn Rodrigues
2017-04-04 7:58 ` Jan Kara
2017-04-04 8:41 ` Christoph Hellwig
2017-04-04 18:41 ` Goldwyn Rodrigues
2017-04-10 7:45 ` Christoph Hellwig
[not found] ` <20170410074539.GA18250-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
2017-04-10 12:37 ` Jan Kara
2017-04-10 14:39 ` Christoph Hellwig
2017-04-10 15:13 ` Jan Kara
2017-04-03 18:53 ` [PATCH 7/8] nowait aio: xfs Goldwyn Rodrigues
2017-04-04 6:52 ` Christoph Hellwig
[not found] ` <20170404065211.GD21942-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
2017-04-06 22:54 ` Darrick J. Wong
2017-04-07 11:34 ` Goldwyn Rodrigues [this message]
2017-04-07 15:08 ` Darrick J. Wong
-- strict thread matches above, loose matches on Subject: below --
2017-05-09 12:22 [PATCH 0/8 v7] No wait AIO Goldwyn Rodrigues
2017-05-09 12:22 ` [PATCH 7/8] nowait aio: xfs Goldwyn Rodrigues
2017-05-11 7:45 ` Christoph Hellwig
2017-04-14 12:02 [PATCH 0/8 v6] No wait AIO Goldwyn Rodrigues
2017-04-14 12:02 ` [PATCH 7/8] nowait aio: xfs Goldwyn Rodrigues
2017-04-19 6:45 ` Christoph Hellwig
2017-03-15 21:50 [PATCH 0/8 v3] No wait AIO Goldwyn Rodrigues
2017-03-15 21:51 ` [PATCH 7/8] nowait aio: xfs Goldwyn Rodrigues
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