| Message ID | 149369654638.5146.3067734913419940612.stgit@noble (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Looks fine,
Reviewed-by: Christoph Hellwig <hch@lst.de>
On Tue, May 02, 2017 at 01:42:26PM +1000, NeilBrown wrote: > blk_bio_segment_split() makes sure bios have no more than > BIO_MAX_PAGES entries in the bi_io_vec. > This was done because bio_clone_bioset() (when given a > mempool bioset) could not handle larger io_vecs. > > No driver uses bio_clone_bioset() any more, they all > use bio_clone_fast() if anything, and bio_clone_fast() > doesn't clone the bi_io_vec. Maybe in future, some drivers still may try to use bio_clone_bioset() again, I suggest to add some comments on bio_clone_bioset() to make this usage explicitly. Also better to trigger a warning if a big src bio is passed to bio_clone_bioset(). Thanks, Ming
On Tue, May 02 2017, Ming Lei wrote: > On Tue, May 02, 2017 at 01:42:26PM +1000, NeilBrown wrote: >> blk_bio_segment_split() makes sure bios have no more than >> BIO_MAX_PAGES entries in the bi_io_vec. >> This was done because bio_clone_bioset() (when given a >> mempool bioset) could not handle larger io_vecs. >> >> No driver uses bio_clone_bioset() any more, they all >> use bio_clone_fast() if anything, and bio_clone_fast() >> doesn't clone the bi_io_vec. > > Maybe in future, some drivers still may try to use > bio_clone_bioset() again, I suggest to add some comments > on bio_clone_bioset() to make this usage explicitly. Also > better to trigger a warning if a big src bio is passed to > bio_clone_bioset(). There are now just two users for bio_clone_bioset(): bounce.c and btrfs. Christoph wants to get rid of bounce.c, which would leave one. I'd have to drill into the btrfs code to be sure, but it might be that btrfs only needs bio_clone_fast(). That would leave zero users. Then we wouldn't need a warning at all. So I agree that we need to guard against future incorrect usage. I'm not yet sure what the best approach is. Thanks, NeilBrown
On Wed, May 03, 2017 at 08:54:55AM +1000, NeilBrown wrote: > On Tue, May 02 2017, Ming Lei wrote: > > > On Tue, May 02, 2017 at 01:42:26PM +1000, NeilBrown wrote: > >> blk_bio_segment_split() makes sure bios have no more than > >> BIO_MAX_PAGES entries in the bi_io_vec. > >> This was done because bio_clone_bioset() (when given a > >> mempool bioset) could not handle larger io_vecs. > >> > >> No driver uses bio_clone_bioset() any more, they all > >> use bio_clone_fast() if anything, and bio_clone_fast() > >> doesn't clone the bi_io_vec. > > > > Maybe in future, some drivers still may try to use > > bio_clone_bioset() again, I suggest to add some comments > > on bio_clone_bioset() to make this usage explicitly. Also > > better to trigger a warning if a big src bio is passed to > > bio_clone_bioset(). > > There are now just two users for bio_clone_bioset(): bounce.c and btrfs. > > Christoph wants to get rid of bounce.c, which would leave one. > > I'd have to drill into the btrfs code to be sure, but it might be that > btrfs only needs bio_clone_fast(). That would leave zero users. > Then we wouldn't need a warning at all. > > So I agree that we need to guard against future incorrect usage. I'm not > yet sure what the best approach is. I think it is helpful to simply comment this function as obsolete. Thanks, Ming
diff --git a/block/blk-merge.c b/block/blk-merge.c index e7862e9dcc39..cea544ec5d96 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -108,25 +108,9 @@ static struct bio *blk_bio_segment_split(struct request_queue *q, bool do_split = true; struct bio *new = NULL; const unsigned max_sectors = get_max_io_size(q, bio); - unsigned bvecs = 0; bio_for_each_segment(bv, bio, iter) { /* - * With arbitrary bio size, the incoming bio may be very - * big. We have to split the bio into small bios so that - * each holds at most BIO_MAX_PAGES bvecs because - * bio_clone_bioset() can fail to allocate big bvecs. - * - * Those drivers which will need to use bio_clone_bioset() - * should tell us in some way. For now, impose the - * BIO_MAX_PAGES limit on all queues. - * - * TODO: handle users of bio_clone_bioset() differently. - */ - if (bvecs++ >= BIO_MAX_PAGES) - goto split; - - /* * If the queue doesn't support SG gaps and adding this * offset would create a gap, disallow it. */
blk_bio_segment_split() makes sure bios have no more than BIO_MAX_PAGES entries in the bi_io_vec. This was done because bio_clone_bioset() (when given a mempool bioset) could not handle larger io_vecs. No driver uses bio_clone_bioset() any more, they all use bio_clone_fast() if anything, and bio_clone_fast() doesn't clone the bi_io_vec. The main user of of bio_clone_bioset() at this level is bounce.c, and bouncing now happens before blk_bio_segment_split(), so that is not of concern. So remove the big helpful comment and the code. Signed-off-by: NeilBrown <neilb@suse.com> --- block/blk-merge.c | 16 ---------------- 1 file changed, 16 deletions(-)