On Fri, Jun 18, 2010 at 10:29 PM, Kyungmin Park <kmpark@xxxxxxxxxxxxx> wrote: > On Fri, Jun 18, 2010 at 4:22 AM, Chris Mason <chris.mason@xxxxxxxxxx> wrote: >> 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. > > I tested btrfs on MMC with discard support and get failed. you can > find a scenario and details at btrfs mailing list. > I'll check it with this patch. > Please note that MMC don't have any queue at internal as SSD. > It's same it failed to use discard on MMC with btrfs. Thank you, Kyungmin Park > -- 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
