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| author |   Mike Snitzer <snitzer@redhat.com> | 2014-10-09 19:32:22 -0400 |
|---|---|---|
| committer | Mike Snitzer <snitzer@redhat.com> | 2014-11-10 15:25:27 -0500 |
| commit | 148e51baf8e7ae2070ec47c2a0ec05ddf6a47da1 (patch) | |
| tree | bf734d271d8f30aa41a4fd9439133f4398ff6d44 /drivers/md | |
| parent | dm thin: adjust max_sectors_kb based on thinp blocksize (diff) | |
| download | linux-dev-148e51baf8e7ae2070ec47c2a0ec05ddf6a47da1.tar.xz linux-dev-148e51baf8e7ae2070ec47c2a0ec05ddf6a47da1.zip | |
dm: improve documentation and code clarity in dm_merge_bvec
These code changes do not introduce a functional change.
But bio_add_page() will never attempt to build up a bio larger than
queue_max_sectors(). Similarly, bio_get_nr_vecs() is also bound by
queue_max_sectors(). Therefore, there is no point in allowing
dm_merge_bvec() to answer "how many sectors can a bio have at this
offset?" with anything larger than queue_max_sectors(). Using
queue_max_sectors() rather than BIO_MAX_SECTORS serves to more
accurately convey the limits that are being imposed.
Also, use unlikely() to clarify the fact that the defensive code in
dm_merge_bvec() relative to max_size going negative shouldn't ever
happen -- if it does happen there is a bug in the block layer for
requesting larger than dm_merge_bvec()'s initial response for a given
offset. Also, update a comment in dm_merge_bvec() relative to
max_hw_sectors_kb. And fix empty newline whitespace.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Diffstat (limited to 'drivers/md')
| -rw-r--r-- | drivers/md/dm.c | 12 |
1 files changed, 6 insertions, 6 deletions
diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 58f3927fd7cc..0fee0e54d36f 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -1607,9 +1607,9 @@ static int dm_merge_bvec(struct request_queue *q, * Find maximum amount of I/O that won't need splitting */ max_sectors = min(max_io_len(bvm->bi_sector, ti), - (sector_t) BIO_MAX_SECTORS); + (sector_t) queue_max_sectors(q)); max_size = (max_sectors << SECTOR_SHIFT) - bvm->bi_size; - if (max_size < 0) + if (unlikely(max_size < 0)) /* this shouldn't _ever_ happen */ max_size = 0; /* @@ -1621,10 +1621,10 @@ static int dm_merge_bvec(struct request_queue *q, max_size = ti->type->merge(ti, bvm, biovec, max_size); /* * If the target doesn't support merge method and some of the devices - * provided their merge_bvec method (we know this by looking at - * queue_max_hw_sectors), then we can't allow bios with multiple vector - * entries. So always set max_size to 0, and the code below allows - * just one page. + * provided their merge_bvec method (we know this by looking for the + * max_hw_sectors that dm_set_device_limits may set), then we can't + * allow bios with multiple vector entries. So always set max_size + * to 0, and the code below allows just one page. */ else if (queue_max_hw_sectors(q) <= PAGE_SIZE >> 9) max_size = 0; |