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

To: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Subject: Re: Ext4 and xfs problems in dm-thin on allocation and discard
From: Mike Snitzer <snitzer@xxxxxxxxxx>
Date: Mon, 2 Jul 2012 09:00:34 -0400
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, Spelic <spelic@xxxxxxxxxxxxx>, device-mapper development <dm-devel@xxxxxxxxxx>, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, axboe@xxxxxxxxx, hch@xxxxxxxxxxxxx, "Martin K. Petersen" <martin.petersen@xxxxxxxxxx>
In-reply-to: <4FF06480.6030109@xxxxxxxxxx>
References: <4FDF9EBE.2030809@xxxxxxxxxxxxx> <20120619015745.GJ25389@dastard> <4FE1BDF3.4080702@xxxxxxxxxxxxx> <20120620225327.GL30705@dastard> <20120621174742.GA27837@xxxxxxxxxx> <4FF06480.6030109@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Sun, Jul 01 2012 at 10:53am -0400,
Paolo Bonzini <pbonzini@xxxxxxxxxx> 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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