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Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io

To: "hch@xxxxxxxxxxxxx" <hch@xxxxxxxxxxxxx>, "Verma, Vishal L" <vishal.l.verma@xxxxxxxxx>
Subject: Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io
From: Vishal Verma <vishal@xxxxxxxxxx>
Date: Tue, 26 Apr 2016 09:01:32 -0600
Cc: "Wilcox, Matthew R" <matthew.r.wilcox@xxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "linux-block@xxxxxxxxxxxxxxx" <linux-block@xxxxxxxxxxxxxxx>, "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>, "linux-nvdimm@xxxxxxxxxxx" <linux-nvdimm@xxxxxxxxxxx>, "jmoyer@xxxxxxxxxx" <jmoyer@xxxxxxxxxx>, "linux-mm@xxxxxxxxx" <linux-mm@xxxxxxxxx>, "viro@xxxxxxxxxxxxxxxxxx" <viro@xxxxxxxxxxxxxxxxxx>, "axboe@xxxxxx" <axboe@xxxxxx>, "akpm@xxxxxxxxxxxxxxxxxxxx" <akpm@xxxxxxxxxxxxxxxxxxxx>, "linux-fsdevel@xxxxxxxxxxxxxxx" <linux-fsdevel@xxxxxxxxxxxxxxx>, "linux-ext4@xxxxxxxxxxxxxxx" <linux-ext4@xxxxxxxxxxxxxxx>, "david@xxxxxxxxxxxxx" <david@xxxxxxxxxxxxx>, "jack@xxxxxxx" <jack@xxxxxxx>
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In-reply-to: <20160426083332.GB364@xxxxxxxxxxxxx>
References: <1459303190-20072-1-git-send-email-vishal.l.verma@xxxxxxxxx> <1459303190-20072-6-git-send-email-vishal.l.verma@xxxxxxxxx> <x49twj26edj.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> <20160420205923.GA24797@xxxxxxxxxxxxx> <1461434916.3695.7.camel@xxxxxxxxx> <20160425083114.GA27556@xxxxxxxxxxxxx> <1461604476.3106.12.camel@xxxxxxxxx> <20160426083332.GB364@xxxxxxxxxxxxx>
On Tue, 2016-04-26 at 01:33 -0700, hch@xxxxxxxxxxxxx wrote:
> On Mon, Apr 25, 2016 at 05:14:36PM +0000, Verma, Vishal L wrote:
> > 
> > - Application hits EIO doing dax_IO or load/store io
> > 
> > - It checks badblocks and discovers it's files have lost data
> > 
> > - It write()s those sectors (possibly converted to file offsets
> > using
> > fiemap)
> > ?? ?? * This triggers the fallback path, but if the application is
> > doing
> > this level of recovery, it will know the sector is bad, and write
> > the
> > entire sector
> This sounds like a mess.
> 
> > 
> > I think if we want to keep allowing arbitrary alignments for the
> > dax_do_io path, we'd need:
> > 1. To represent badblocks at a finer granularity (likely cache
> > lines)
> > 2. To allow the driver to do IO to a *block device* at sub-sector
> > granularity
> It's not a block device if it supports DAX.ÂÂIt's byte addressable
> memory masquerading as a block device.

Yes but we made that decision a while back with pmem :)
Are you saying it should stop being a block device anymore?

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