Re: [patch v2 2/6] blk: dont allow discard request merge temporarily

[Christoph Hellwig]

On Wed, Mar 21, 2012 at 10:18:54PM -0400, Martin K. Petersen wrote:
> >>>>> "Shaohua" == Shaohua Li <shli@xxxxxxxxxx> writes:
> 
> Shaohua> Enabling discard merge is required for device with slow discard
> Shaohua> (and very helpful for raid),
> 
> Before RAID support there really wasn't much point. That's one of the
> reasons the current discard merge code has survived despite being
> completely broken.

I've actually send repeated bug reports about it beeing broken when
I enabled async discard in XFS which led to merges, and debugged it down
to beeing a problem with merges.  But Jens didn't like my patch to mark
them nomerged, so we still couldn't commit the async discard support for
XFS which would have helped quite a bit with discard performance.

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