Re: block: re-add discard_granularity and alignment checks

[Mike Snitzer]

On Thu, Oct 22 2015 at 12:59pm -0400,
Ming Lin <mlin@xxxxxxxxxx> wrote:

> From: Ming Lin <ming.l@xxxxxxxxxxxxxxx>
> 
> In commit b49a087("block: remove split code in
> blkdev_issue_{discard,write_same}"), discard_granularity and alignment
> checks were removed. Ideally, with bio late splitting, the upper layers
> shouldn't need to depend on device's limits.
> 
> Christoph reported a discard regression on the HGST Ultrastar SN100 NVMe
> device when mkfs.xfs. We have not found the root cause yet.
> 
> This patch re-adds discard_granularity and alignment checks by reverting
> the related changes in commit b49a087. The good thing is now we can
> remove the 2G discard size cap and just use UINT_MAX to avoid bi_size
> overflow.
> 
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Tested-by: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: Ming Lin <ming.l@xxxxxxxxxxxxxxx>

Reviewed-by: Mike Snitzer <snitzer@xxxxxxxxxx>

Thanks!
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