linux-kernel - Re: merging discard request in the block layer

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Message-ID: <20110323130137.GA10455@infradead.org>
Date:	Wed, 23 Mar 2011 09:01:37 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Jens Axboe <jaxboe@...ionio.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: merging discard request in the block layer

On Tue, Mar 22, 2011 at 10:03:57PM +0100, Jens Axboe wrote:
> > That would seem to indicate a bug in the merging logic instead.
> 
> What kind of max discard size does you device have? If the max discard
> size is smaller than the regular request size, this could help.

It's a SCSI device, so the max discard size is a lot larger:

# cat /sys/block/sda/queue/max_sectors_kb
512
# cat /sys/block/sda/queue/max_hw_sectors_kb 
32767
# cat /sys/block/sda/queue/discard_max_bytes 
4294966784

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