On Thu, Jul 05 2012 at 12:01pm -0400, Paolo Bonzini <pbonzini@xxxxxxxxxx> 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 > > block/blk-lib.c | 41 ++++++++++++++++++++++++++++------------- > include/linux/blkdev.h | 10 ++++++++++ > 2 files changed, 38 insertions(+), 13 deletions(-) Hey Jens, Would be great to get these discard fixes in. I know both Christoph and Vivek have reviewed these changes but that isn't reflected in the patch headers. These patches eliminate misaligned discard from being sent to the dm-thinp target. Tested-by: Mike Snitzer <snitzer@xxxxxxxxxx> -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
