Re: merging discard request in the block layer

[Jens Axboe]

On 2011-03-23 14:01, Christoph Hellwig wrote:
> 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

I'll try and throw a synthetic test at it that produces a slew of
discard merging and see what happens.

-- 
Jens Axboe

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