linux-ext4 - Re: Ext4 and xfs problems in dm-thin on allocation and discard

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Message-ID: <20120702130034.GA785@redhat.com>
Date:	Mon, 2 Jul 2012 09:00:34 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Dave Chinner <david@...morbit.com>, Spelic <spelic@...ftmail.org>,
	device-mapper development <dm-devel@...hat.com>,
	linux-ext4@...r.kernel.org, xfs@....sgi.com, axboe@...nel.dk,
	hch@...radead.org,
	"Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: Ext4 and xfs problems in dm-thin on allocation and discard

On Sun, Jul 01 2012 at 10:53am -0400,
Paolo Bonzini <pbonzini@...hat.com> wrote:

> Il 21/06/2012 19:47, Mike Snitzer ha scritto:
> > Paolo Bonzini fixed blkdev_issue_discard to properly align some time
> > ago; unfortunately the patches slipped through the cracks (cc'ing Paolo,
> > Jens, and Christoph).
> > 
> > Here are references to Paolo's patches:
> > 0/2 https://lkml.org/lkml/2012/3/14/323
> > 1/2 https://lkml.org/lkml/2012/3/14/324
> > 2/2 https://lkml.org/lkml/2012/3/14/325
> > 
> > Patch 2/2 specifically addresses the case where:
> >  discard_max_bytes == discard_granularity 
> > 
> > Paolo, any chance you could resend to Jens (maybe with hch's comments on
> > patch#2 accounted for)?  Also, please add hch's Reviewed-by when
> > reposting.
> 
> Sure, I'll do it this week.  I just need to retest.

Great, thanks.

(cc'ing mkp)

One thing that seemed odd was your adjustment for discard_alignment (in
patch 1/2).

I need to better understand how discard_alignment (an offset despite the
name not saying as much) relates to alignment_offset.

Could just be that once a partition tool, or lvm, etc account for
alignment_offset (which they do now) that discard_alignment is
automagically accounted for as a side-effect?

(I haven't actually seen discard_alignment != 0 in the wild)

Mike
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