On Mon, Aug 10, 2015 at 10:41:55PM -0400, Mike Snitzer wrote: > On Mon, Aug 10 2015 at 10:00pm -0400, > Martin K. Petersen <martin.petersen@xxxxxxxxxx> wrote: > > > >>>>> "Ming" == Ming Lin <mlin@xxxxxxxxxx> writes: > > > > Ming> Did you mean still use (UINT_MAX >> 9) in blkdev_issue_discard()? > > > > Ming> But that doesn't work for dm-thinp. See Kent's suggestion to use > > Ming> 1<<31. > > > > I'm not sure why things are not working for dm-thinp. Presumably Kent's > > code would split the discard at a granularity boundary so why would that > > cause problems for dm? > > DM-thinp processes discards internally before it passes them down (if > configured to do so). If a discard is smaller than the granularity of a > thinp block (whose size is configurable) or if the start and end of the > discard's extent is misaligned (relative to the thinp blocks mapped to > the logical extent) then the discard won't actually discard partial > thinp blocks. This kind of logic really doesn't belong in dm - if it's needed, it really belongs in bio_split() (which is supposed to work correctly for discards - so if it is needed, then bio_split() needs fixing...) IMO though it belongs in the driver - if a discard needs to be dropped because it's too small and the hardware can't do it, that should be the driver's responsibility. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
