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From: Jan Kara <jack@suse.cz>
To: Matthew Bobrowski <mbobrowski@mbobrowski.org>
Cc: Jan Kara <jack@suse.cz>,
	linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	tytso@mit.edu, riteshh@linux.ibm.com
Subject: Re: [PATCH 4/5] ext4: introduce direct IO write code path using iomap infrastructure
Date: Thu, 29 Aug 2019 14:38:25 +0200
Message-ID: <20190829123825.GB22939@quack2.suse.cz> (raw)
In-Reply-To: <20190829114515.GB2486@poseidon.bobrowski.net>

On Thu 29-08-19 21:45:17, Matthew Bobrowski wrote:
> > > @@ -3581,10 +3611,10 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> > >  		iomap->type = delalloc ? IOMAP_DELALLOC : IOMAP_HOLE;
> > >  		iomap->addr = IOMAP_NULL_ADDR;
> > >  	} else {
> > > -		if (map.m_flags & EXT4_MAP_MAPPED) {
> > > -			iomap->type = IOMAP_MAPPED;
> > > -		} else if (map.m_flags & EXT4_MAP_UNWRITTEN) {
> > > +		if (map.m_flags & EXT4_MAP_UNWRITTEN) {
> > >  			iomap->type = IOMAP_UNWRITTEN;
> > > +		} else if (map.m_flags & EXT4_MAP_MAPPED) {
> > > +			iomap->type = IOMAP_MAPPED;
> > >  		} else {
> > >  			WARN_ON_ONCE(1);
> > >  			return -EIO;
> > 
> > Possibly this hunk should go into a separate patch (since this is not
> > directly related with iomap conversion) with a changelog / comment
> > explaining why we need to check EXT4_MAP_UNWRITTEN first.
> 
> But wouldn't doing so break bisection? Seeing as though we needed to
> change this statement specifically to accommodate for the weirdness
> being returned from ext4_map_blocks()? i.e. map.m_flags being set to
> either of the following:
> 
> 	- (EXT4_MAP_NEW | EXT4_MAP_MAPPED)
>         or
>         - (EXT4_MAP_NEW | EXT4_MAP_MAPPED | EXT4_MAP_UNWRITTEN)
> 
> So, if we left the statement in its original form, we'd allocate
> unwritten extents but never actually get around to converting them in
> ext4_dio_write_end_io() as IOMAP_DIO_UNWRITTEN would never be set?

By splitting into a separate patch, I meant that patch would go before this
one. Original code in ext4_iomap_begin() never called ext4_map_blocks()
with a set of flags that can return with both EXT4_MAP_MAPPED and
EXT4_MAP_UNWRITTEN set so that patch would be a no-op but would fix that
landmine you tripped over.

								Honza

-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

  reply index

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-12 12:52 [PATCH 0/5] ext4: direct IO via " Matthew Bobrowski
2019-08-12 12:52 ` [PATCH 1/5] ext4: introduce direct IO read code path using " Matthew Bobrowski
2019-08-12 17:18   ` Christoph Hellwig
2019-08-12 20:17     ` Matthew Wilcox
2019-08-13 10:45       ` Matthew Bobrowski
2019-08-12 12:52 ` [PATCH 2/5] ext4: move inode extension/truncate code out from ext4_iomap_end() Matthew Bobrowski
2019-08-12 17:18   ` Christoph Hellwig
2019-08-13 10:46     ` Matthew Bobrowski
2019-08-28 19:59   ` Jan Kara
2019-08-28 21:54     ` Matthew Bobrowski
2019-08-29  8:18       ` Jan Kara
2019-08-12 12:53 ` [PATCH 3/5] iomap: modify ->end_io() calling convention Matthew Bobrowski
2019-08-12 17:18   ` Christoph Hellwig
2019-08-13 10:43     ` Matthew Bobrowski
2019-08-12 12:53 ` [PATCH 4/5] ext4: introduce direct IO write code path using iomap infrastructure Matthew Bobrowski
2019-08-12 17:04   ` RITESH HARJANI
2019-08-13 12:58     ` Matthew Bobrowski
2019-08-13 14:35       ` Darrick J. Wong
2019-08-14  9:51         ` Matthew Bobrowski
2019-08-12 17:34   ` Christoph Hellwig
2019-08-13 10:45     ` Matthew Bobrowski
2019-08-28 20:26   ` Jan Kara
2019-08-28 22:32     ` Dave Chinner
2019-08-29  8:03       ` Jan Kara
2019-08-29 11:47       ` Matthew Bobrowski
2019-08-29 11:45     ` Matthew Bobrowski
2019-08-29 12:38       ` Jan Kara [this message]
2019-08-12 12:53 ` [PATCH 5/5] ext4: clean up redundant buffer_head direct IO code Matthew Bobrowski
2019-08-12 17:31 ` [PATCH 0/5] ext4: direct IO via iomap infrastructure RITESH HARJANI
2019-08-13 11:10   ` Matthew Bobrowski
2019-08-13 12:27     ` RITESH HARJANI
2019-08-14  9:48       ` Matthew Bobrowski
2019-08-14 11:58         ` RITESH HARJANI
2019-08-21 13:14       ` Matthew Bobrowski
2019-08-22 12:00         ` Matthew Bobrowski
2019-08-22 14:11           ` Ritesh Harjani
2019-08-24  3:18             ` Matthew Bobrowski
2019-08-24  3:55               ` Darrick J. Wong
2019-08-24 23:04                 ` Christoph Hellwig
2019-08-27  9:52                   ` Matthew Bobrowski
2019-08-28 12:05                     ` Matthew Bobrowski
2019-08-28 14:27                       ` Theodore Y. Ts'o
2019-08-28 18:02                         ` Jan Kara
2019-08-29  6:36                           ` Christoph Hellwig
2019-08-29 11:20                             ` Matthew Bobrowski
2019-08-29 14:41                               ` Christoph Hellwig
2019-08-23 13:43           ` [RFC 1/1] ext4: PoC implementation of option-1 Ritesh Harjani
2019-08-23 13:49             ` Ritesh Harjani

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