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Re: [PATCH 4/5] dax: use sb_issue_zerout instead of calling dax_clear_se

To: "Verma, Vishal L" <vishal.l.verma@xxxxxxxxx>
Subject: Re: [PATCH 4/5] dax: use sb_issue_zerout instead of calling dax_clear_sectors
From: Jan Kara <jack@xxxxxxx>
Date: Wed, 30 Mar 2016 09:49:26 +0200
Cc: "Williams, Dan J" <dan.j.williams@xxxxxxxxx>, "linux-block@xxxxxxxxxxxxxxx" <linux-block@xxxxxxxxxxxxxxx>, "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>, "linux-mm@xxxxxxxxx" <linux-mm@xxxxxxxxx>, "viro@xxxxxxxxxxxxxxxxxx" <viro@xxxxxxxxxxxxxxxxxx>, "axboe@xxxxxx" <axboe@xxxxxx>, "akpm@xxxxxxxxxxxxxxxxxxxx" <akpm@xxxxxxxxxxxxxxxxxxxx>, "linux-nvdimm@xxxxxxxxxxxx" <linux-nvdimm@xxxxxxxxxxxx>, "linux-fsdevel@xxxxxxxxxxxxxxx" <linux-fsdevel@xxxxxxxxxxxxxxx>, "ross.zwisler@xxxxxxxxxxxxxxx" <ross.zwisler@xxxxxxxxxxxxxxx>, "linux-ext4@xxxxxxxxxxxxxxx" <linux-ext4@xxxxxxxxxxxxxxx>, "Wilcox, Matthew R" <matthew.r.wilcox@xxxxxxxxx>, "david@xxxxxxxxxxxxx" <david@xxxxxxxxxxxxx>, "jack@xxxxxxx" <jack@xxxxxxx>
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User-agent: Mutt/1.5.24 (2015-08-30)
On Tue 29-03-16 18:57:16, Verma, Vishal L wrote:
> On Mon, 2016-03-28 at 16:34 -0700, Dan Williams wrote:
> 
> <>
> 
> > Seems kind of sad to fail the fault due to a bad block when we were
> > going to zero it anyway, right?  I'm not seeing a compelling reason to
> > keep any zeroing in fs/dax.c.
> 
> Agreed - but how do we do this? clear_pmem needs to be able to clear an
> arbitrary number of bytes, but to go through the driver, we'd need to
> send down a bio? If only the driver had an rw_bytes like interface that
> could be used by anyone... :)

Actually, my patches for page fault locking remove zeroing from
dax_insert_mapping() and __dax_pmd_fault() - the zeroing now happens from
the filesystem only and the zeroing in those two functions is just a dead
code...

                                                                Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR

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