linux-ext4 - Re: [PATCH 4/5] dax: use sb_issue_zerout instead of calling dax_clear

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Message-ID: <20160330074926.GC12776@quack.suse.cz>
Date:	Wed, 30 Mar 2016 09:49:26 +0200
From:	Jan Kara <jack@...e.cz>
To:	"Verma, Vishal L" <vishal.l.verma@...el.com>
Cc:	"Williams, Dan J" <dan.j.williams@...el.com>,
	"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
	"xfs@....sgi.com" <xfs@....sgi.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"axboe@...com" <axboe@...com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"ross.zwisler@...ux.intel.com" <ross.zwisler@...ux.intel.com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>,
	"david@...morbit.com" <david@...morbit.com>,
	"jack@...e.cz" <jack@...e.cz>
Subject: Re: [PATCH 4/5] dax: use sb_issue_zerout instead of calling
 dax_clear_sectors

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@...e.com>
SUSE Labs, CR
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