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Message-ID: <50195026.4030901@kernel.dk>
Date: Wed, 01 Aug 2012 17:49:58 +0200
From: Jens Axboe <axboe@...nel.dk>
To: Mike Snitzer <snitzer@...hat.com>
CC: linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
martin.petersen@...cle.com, david@...morbit.com, xfs@....sgi.com,
dm-devel@...hat.com, hch@....de, vgoyal@...hat.com
Subject: Re: [PATCH v3 0/2] block: improvements for discard alignment
On 08/01/2012 03:40 PM, Mike Snitzer wrote:
> On Thu, Jul 05 2012 at 12:01pm -0400,
> Paolo Bonzini <pbonzini@...hat.com> wrote:
>
>> When a disk has a large discard_granularity, discards are not split with
>> optimal alignment; the pessimization gets bigger as discard_granularity
>> and max_discard_sectors become closer.
>>
>> Take the limit case of discard_granularity == max_discard_sectors == 64.
>> Then, if a request is submitted for 256 sectors 2..257 it will be split
>> like this: 2..65, 66..129, 130..193, 194..257. None of these requests
>> is aligned, so in fact you might end up with no discarded logical blocks
>> at all. With this patch, the split will be 2..63, 64..127, 128..191,
>> 192..255, 256..257. The patches also take the discard_alignment into
>> consideration.
>>
>> Patch 1 adjusts the computation of the granularity-adjusted
>> max_discard_sectors so that it prepares for the new code in patch 2,
>> which actually adjusts the split.
>>
>> v2->v3: drop addition of queue/discard_alignment to sysfs, use
>> correct alignment for partitions
>>
>> Paolo Bonzini (2):
>> block: reorganize rounding of max_discard_sectors
>> block: split discard into aligned requests
>>
>> block/blk-lib.c | 41 ++++++++++++++++++++++++++++-------------
>> include/linux/blkdev.h | 10 ++++++++++
>> 2 files changed, 38 insertions(+), 13 deletions(-)
>
> Hey Jens,
>
> Would be great to get these discard fixes in. I know both Christoph and
> Vivek have reviewed these changes but that isn't reflected in the patch
> headers.
>
> These patches eliminate misaligned discard from being sent to the
> dm-thinp target.
>
> Tested-by: Mike Snitzer <snitzer@...hat.com>
Sure, I'll get it in for this series. Thanks.
--
Jens Axboe
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