On Thu, Jun 17, 2010 at 06:54:53PM +0200, Christoph Hellwig wrote: > On Thu, Jun 17, 2010 at 10:10:18AM +0200, Jens Axboe wrote: > > Thanks, applied. There was a recent problem report on btrfs using > > discard, could possibly explain it if Chris assumed it was a full > > barrier. > > We actually have a much bigger issue with the DISCARD_BARRIER type. > If the discard request needs to get split into multiple smaller ones > we don't keep the queue drained atomically around them, so requests > could sneak inbetween them. Depending on how the realtime discard > is implemented that could cause issues. In my XFS prototype for it > I only deleted the extents from the tracking betree after the discard > request has returned, but other filesystems rely on full barrier > semantics of DISCARD_BARRIER this could cause real problems. btrfs needs to know that a write after the discard returns won't cross the discard, but beyond that we're happy with anything. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
