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From: Goldwyn Rodrigues <rgoldwyn@suse.de>
To: Christoph Hellwig <hch@infradead.org>
Cc: Ritesh Harjani <riteshh@linux.ibm.com>,
	linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	darrick.wong@oracle.com
Subject: Re: [PATCH v2] iomap: return partial I/O count on error in iomap_dio_bio_actor
Date: Tue, 25 Feb 2020 20:55:31 -0600	[thread overview]
Message-ID: <20200226025531.k7miaxfu2yzt3kh6@fiona> (raw)
In-Reply-To: <20200225205342.GA12066@infradead.org>

On 12:53 25/02, Christoph Hellwig wrote:
> On Fri, Feb 21, 2020 at 10:21:04AM +0530, Ritesh Harjani wrote:
> > >   		if (dio->error) {
> > >   			iov_iter_revert(dio->submit.iter, copied);
> > > -			copied = ret = 0;
> > > +			ret = 0;
> > >   			goto out;
> > >   		}
> > 
> > But if I am seeing this correctly, even after there was a dio->error
> > if you return copied > 0, then the loop in iomap_dio_rw will continue
> > for next iteration as well. Until the second time it won't copy
> > anything since dio->error is set and from there I guess it may return
> > 0 which will break the loop.
> 
> In addition to that copied is also iov_iter_reexpand call.  We don't
> really need the re-expand in case of errors, and in fact we also
> have the iov_iter_revert call before jumping out, so this will
> need a little bit more of an audit and properly documented in the
> commit log.
> 
> > 
> > Is this the correct flow? Shouldn't the while loop doing
> > iomap_apply in iomap_dio_rw should also break in case of
> > dio->error? Or did I miss anything?
> 
> We'd need something there iff we care about a good number of written
> in case of the error.  Goldwyn, can you explain what you need this
> number for in btrfs?  Maybe with a pointer to the current code base?

btrfs needs to account for the bytes "processed", failed or
uptodate. This is currently performed in
fs/btrfs/inode.c:__end_write_update_ordered().

For the current development version, how I am using it is in my git
branch btrfs-iomap-dio [1]. The related commit besides this patch
is:

9aeb2b31d10b ("btrfs: Use ->iomap_end() instead of btrfs_dio_data")

[1] https://github.com/goldwynr/linux/tree/btrfs-iomap-dio

-- 
Goldwyn

  parent reply	other threads:[~2020-02-26  2:55 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-20 15:23 [PATCH v2] iomap: return partial I/O count on error in iomap_dio_bio_actor Goldwyn Rodrigues
2020-02-20 17:42 ` Matthew Wilcox
2020-02-21  2:06   ` Goldwyn Rodrigues
2020-02-21  4:51 ` Ritesh Harjani
2020-02-21 12:48   ` Goldwyn Rodrigues
2020-02-25 20:53   ` Christoph Hellwig
2020-02-26  2:12     ` Damien Le Moal
2020-02-26  2:55     ` Goldwyn Rodrigues [this message]
2020-02-28 19:44     ` Goldwyn Rodrigues
2020-02-28 19:59       ` Matthew Wilcox
2020-02-28 20:35         ` Goldwyn Rodrigues
2020-03-02 13:31           ` Christoph Hellwig
2020-02-21 13:14 ` David Sterba
2020-02-20 15:24 Goldwyn Rodrigues
2020-03-19 15:08 Goldwyn Rodrigues
2020-03-20 14:05 ` Christoph Hellwig
2020-03-20 14:23   ` Josef Bacik
2020-03-20 14:35     ` Christoph Hellwig
2020-03-20 15:35       ` Goldwyn Rodrigues

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