Re: [PATCH v6 05/11] block: remove split code in blkdev_issue_{discard,write_same}

[Christoph Hellwig]

On Wed, Aug 12, 2015 at 12:07:15AM -0700, Ming Lin wrote:
> From: Ming Lin <ming.l@xxxxxxxxxxxxxxx>
> 
> The split code in blkdev_issue_{discard,write_same} can go away
> now that any driver that cares does the split. We have to make
> sure bio size doesn't overflow.
> 
> For discard, we set max discard sectors to (1<<31)>>9 to ensure
> it doesn't overflow bi_size and hopefully it is of the proper
> granularity as long as the granularity is a power of two.

This ends up breaking discard on NVMe devices for a me.  An mkfs.xfs
which does a discard of the whole device now hangs the system.
Something in here makes it send discard command that the device doesn't
like and the aborts don't seem to help either, although that might be
an issue with the abort handling in the driver.

Just a heads up for now, once I get a bit more time I'll try to collect
a blktrace to figure out how the commands sent to the driver look
different before and after the patch.
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