On Mon, Apr 11 2022 at 12:58P -0400,
Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
> On Sat, Apr 09 2022 at 1:15P -0400,
> Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
>
> > On Fri, Apr 08, 2022 at 11:42:51AM -0400, Mike Snitzer wrote:
> > > I think we can achieve the goal of efficient cloning/remapping for
> > > both usecases simply by splitting out the bio_set_dev() and leaving it
> > > to the caller to pick which interface to use (e.g. clone vs
> > > clone_and_remap).
> >
> > You can just pass a NULL bdev to bio_alloc_clone/bio_init_clone.
> > I've been hoping to get rid of that, but if we have a clear use case
> > it will have to stay.
>
> DM core is just using bio_alloc_clone. And bio_alloc_bioset() allows
> bdev to be NULL -- so you're likely referring to that (which will skip
> bio_init's bio_associate_blkg).
...
> diff --git a/block/bio.c b/block/bio.c
> index 7892f1108ca6..0340acc283a0 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -772,14 +772,16 @@ static int __bio_clone(struct bio *bio, struct bio *bio_src, gfp_t gfp)
> bio_set_flag(bio, BIO_CLONED);
> if (bio_flagged(bio_src, BIO_THROTTLED))
> bio_set_flag(bio, BIO_THROTTLED);
> - if (bio->bi_bdev == bio_src->bi_bdev &&
> - bio_flagged(bio_src, BIO_REMAPPED))
> - bio_set_flag(bio, BIO_REMAPPED);
> bio->bi_ioprio = bio_src->bi_ioprio;
> bio->bi_iter = bio_src->bi_iter;
>
> - bio_clone_blkg_association(bio, bio_src);
> - blkcg_bio_issue_init(bio);
> + if (bio->bi_bdev == bio_src->bi_bdev) {
> + if (bio_flagged(bio_src, BIO_REMAPPED))
> + bio_set_flag(bio, BIO_REMAPPED);
> +
> + bio_clone_blkg_association(bio, bio_src);
> + blkcg_bio_issue_init(bio);
> + }
>
> if (bio_crypt_clone(bio, bio_src, gfp) < 0)
> return -ENOMEM;
>
> Think this will fix some of the performance penalty of redundant blkcg
> initialization that I reported (though like was also discussed: more
> work likely needed to further optimize bio_associate_blkg).
Looking closer at the case where bio_{alloc,init}_clone are passed a
bdev, bio_init() will call bio_associate_blkg() so the __bio_clone()
work to do anything with blkbg isn't needed at all. So this patch is
best:
diff --git a/block/bio.c b/block/bio.c
index 7892f1108ca6..6980f1b4b0f4 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -778,9 +778,6 @@ static int __bio_clone(struct bio *bio, struct bio *bio_src, gfp_t gfp)
bio->bi_ioprio = bio_src->bi_ioprio;
bio->bi_iter = bio_src->bi_iter;
- bio_clone_blkg_association(bio, bio_src);
- blkcg_bio_issue_init(bio);
-
if (bio_crypt_clone(bio, bio_src, gfp) < 0)
return -ENOMEM;
if (bio_integrity(bio_src) &&
