Hi Shaohua, I've been doing some testing and discovered a problem with your discard support for RAID5.
The code in blkdev_issue_discard assumes that the 'granularity' is a power of 2, and for example subtracts 1 to get a mask. However RAID5 sets the granularity to be the stripe size which often is not a power of two. When this happens you can easily get into an infinite loop. I suspect that to make this work properly, blkdev_issue_discard will need to be changed to allow 'granularity' to be an arbitrary value. When it is a power of two, the current masking can be used. When it is anything else, it will need to use sector_div(). Could you look into this please? Thanks, NeilBrown
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