On Sun, 27 Jun 2010 11:26:52 +0200 Christoph Hellwig <hch@xxxxxx> wrote: > On Sun, Jun 27, 2010 at 05:49:29PM +0900, FUJITA Tomonori wrote: > > On Sat, 26 Jun 2010 15:56:50 -0400 > > Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > > > > > Fix leaks introduced via "block: don't allocate a payload for discard > > > request" commit a1d949f5f44. > > > > > > sd_done() is not called for REQ_TYPE_BLOCK_PC commands so cleanup > > > discard request's payload directly in scsi_finish_command(). > > > > Instead of adding another discard hack to scsi_finish_command(), how > > about converting discard to REQ_TYPE_FS request? discard is FS request > > from the perspective of the block layer. It also fixes a problem that > > discard isn't retried in the case of UNIT ATTENTION. > > > > I think that we can get more cleaner code if we handle discard as > > normal (fs) request in the block layer (and scsi-ml). We need more > > changes but this patch is the first step. > > Making discard a REQ_TYPE_FS inside scsi (it already is before entering > sd_prep_fn) means we'll need to special case it all over the I/O > submission and completion path. Having the payload length not matching Hmm, my patch doesn't add any special case in scsi submission and completion. sd_prep_fn already has a hack for discard to set bi->bi_size to rq->__data_size so scsi can tell the block layer to finish discard requests. Adding another special case for discard to scsi_io_completion() doesn't look good. About the block layer, we already have special case for discard everywhere (rq->cmd_flags & REQ_DISCARD). > the transfer length is something we don't expect for FS requests. Yeah, that's tricky. I'm not sure yet which is better; change how the block layer handles the transfer length or let the lower layer to add pages (as we do now). > > index e16185b..9e15c46 100644 > > --- a/block/blk-lib.c > > +++ b/block/blk-lib.c > > @@ -20,6 +20,10 @@ static void blkdev_discard_end_io(struct bio *bio, int err) > > if (bio->bi_private) > > complete(bio->bi_private); > > > > + /* free the page that the lower layer allocated */ > > + if (bio_page(bio)) > > + __free_page(bio_page(bio)); > > + > > This is exactly what this patchkit gets rid off. Having a payload > page that the caller tracks (previously fully, with this patch only for > freeing) makes DM's life a lot harder. Remember we don't actually store > any payload in there before entering sd_prep_fn - it's just that the > scsi commands implementing discards need some payload - either a sector > sizes zero filled buffer for WRITE SAME, or an LBA/len encoding inside > the payload for UNMAP. It's so bad if the block layer frees pages that the lower layer allocates? I thought it's ok if the block layer doesn't allocate. It's better if sd_done() frees a page? As my patch does, if we handle discard as FS in scsi-ml, sd_done() is called. > > - rq->cmd_type = REQ_TYPE_BLOCK_PC; > > + rq->cmd_type = REQ_TYPE_FS; > > No need to set REQ_TYPE_FS here, it's already set up that way. Oops, sure. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
