linux-kernel - Re: [PATCH v2 5/5] dax: handle media errors in dax_do

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Message-ID: <1461682892.26226.23.camel@kernel.org>
Date:	Tue, 26 Apr 2016 09:01:32 -0600
From:	Vishal Verma <vishal@...nel.org>
To:	"hch@...radead.org" <hch@...radead.org>,
	"Verma, Vishal L" <vishal.l.verma@...el.com>
Cc:	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
	"xfs@....sgi.com" <xfs@....sgi.com>,
	"linux-nvdimm@...1.01.org" <linux-nvdimm@...1.01.org>,
	"jmoyer@...hat.com" <jmoyer@...hat.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-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"david@...morbit.com" <david@...morbit.com>,
	"jack@...e.cz" <jack@...e.cz>
Subject: Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io

On Tue, 2016-04-26 at 01:33 -0700, hch@...radead.org 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.  It'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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