On Thu, Jul 05, 2012 at 06:01:42PM +0200, Paolo Bonzini wrote: > When a disk has a large discard_granularity, discards are not split with > optimal alignment; the pessimization gets bigger as discard_granularity > and max_discard_sectors become closer. > > Take the limit case of discard_granularity == max_discard_sectors == 64. > Then, if a request is submitted for 256 sectors 2..257 it will be split > like this: 2..65, 66..129, 130..193, 194..257. None of these requests > is aligned, so in fact you might end up with no discarded logical blocks > at all. With this patch, the split will be 2..63, 64..127, 128..191, > 192..255, 256..257. The patches also take the discard_alignment into > consideration. > > Patch 1 adjusts the computation of the granularity-adjusted > max_discard_sectors so that it prepares for the new code in patch 2, > which actually adjusts the split. > > v2->v3: drop addition of queue/discard_alignment to sysfs, use > correct alignment for partitions > > Paolo Bonzini (2): > block: reorganize rounding of max_discard_sectors > block: split discard into aligned requests Looks good to me. Did little testing with scsi_debug with discard_alignment=0 and discard_alignment=7 (sectors). We seem to be aligning requests better now. Acked-by: Vivek Goyal <vgoyal@xxxxxxxxxx> Thanks Vivek -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
