From: Jens Axboe <axboe@kernel.dk>
To: Adrian Hunter <adrian.hunter@nokia.com>
Cc: linux-kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] block: prevent merges of discard and write requests
Date: Sat, 25 Sep 2010 12:40:48 +0200 [thread overview]
Message-ID: <4C9DD1B0.9020902@kernel.dk> (raw)
In-Reply-To: <1285411002-22924-1-git-send-email-adrian.hunter@nokia.com>
On 2010-09-25 12:36, Adrian Hunter wrote:
> Add logic to prevent two I/O requests being merged if
> only one of them is a discard. Ditto secure discard.
>
> Without this fix, it is possible for write requests
> to transform into discard requests. For example:
>
> Submit bio 1 to discard 8 sectors from sector n
> Submit bio 2 to write 8 sectors from sector n + 16
> Submit bio 3 to write 8 sectors from sector n + 8
>
> Bio 1 becomes request 1. Bio 2 becomes request 2.
> Bio 3 is merged with request 2, and then subsequently
> request 2 is merged with request 1 resulting in just
> one I/O request which discards all 24 sectors.
Wow, that's a disaster. We can now have requests in the
same direction and of the same type (fs), but not mergeable.
I would move the check up above the position calculations.
I will apply this and upstream it right away. Thanks a lot!
--
Jens Axboe
next prev parent reply other threads:[~2010-09-25 10:40 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-25 10:36 [PATCH] block: prevent merges of discard and write requests Adrian Hunter
2010-09-25 10:40 ` Jens Axboe [this message]
2010-09-27 3:30 ` Kyle McMartin
2010-09-27 4:59 ` Jens Axboe
2010-09-27 5:02 ` Kyle McMartin
2010-09-27 5:12 ` Mike Snitzer
2010-09-27 5:26 ` Mike Snitzer
2010-09-27 6:08 ` Jens Axboe
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