On Thu, Nov 01, 2012 at 05:38:54PM +1100, NeilBrown wrote: > > 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(). Yep, looks we need use sector_div. And this isn't the only problem. discard request can be merged, and the merge check only checks max_discard_sectors. That means the split requests in blkdev_issue_discard can be merged again. The split nerver works. I'm wondering what's purpose of discard_alignment and discard_granularity. Are there devices with discard_granularity not 1 sector? If bio isn't discard aligned, what device will do? Further, why driver handles alignment/granularity if device will ignore misaligned request. Jens, can you share some hints please? Thanks, Shaohua -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
