Re: [PATCH 07/10] block: kill merge_bvec_fn() completely
From: Ming Lin <mlin@kernel.org>
Date: 2015-05-04 07:47:54
Also in:
ceph-devel, dm-devel, lkml
Subsystem:
software raid (multiple disks) support, the rest · Maintainers:
Song Liu, Yu Kuai, Linus Torvalds
On 04/28/2015 03:09 PM, NeilBrown wrote:
On Mon, 27 Apr 2015 23:48:34 -0700 Ming Lin [off-list ref] wrote:quoted
From: Kent Overstreet <redacted> As generic_make_request() is now able to handle arbitrarily sized bios, it's no longer necessary for each individual block driver to define its own ->merge_bvec_fn() callback. Remove every invocation completely.This patch it just a little premature I think. md/raid5 still assumes read requests will mostly fit within a single chunk (which merge_bvec_fn encourages) so they can be serviced without using the stripe-cache. You've just broken that assumption. I think 'chunk_aligned_read' needs to get a loop using bio_split, a bit like raid0, first.
How about below? drivers/md/raid5.c | 35 ++++++++++++++++++++++++++++++++--- 1 file changed, 32 insertions(+), 3 deletions(-)
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index e42b624..2ddfa1e 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c@@ -4709,7 +4709,7 @@ static void raid5_align_endio(struct bio *bi, int error) add_bio_to_retry(raid_bi, conf); } -static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio) +static int __chunk_aligned_read(struct mddev *mddev, struct bio *raid_bio) { struct r5conf *conf = mddev->private; int dd_idx;
@@ -4718,7 +4718,7 @@ static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio) sector_t end_sector; if (!in_chunk_boundary(mddev, raid_bio)) { - pr_debug("chunk_aligned_read : non aligned\n"); + pr_debug("__chunk_aligned_read : non aligned\n"); return 0; } /*
@@ -4793,6 +4793,35 @@ static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio) } } +static struct bio *chunk_aligned_read(struct mddev *mddev, struct bio *raid_bio) +{ + struct bio *split; + + do { + sector_t sector = raid_bio->bi_iter.bi_sector; + unsigned chunk_sects = mddev->chunk_sectors; + + unsigned sectors = chunk_sects - + (likely(is_power_of_2(chunk_sects)) + ? (sector & (chunk_sects-1)) + : sector_div(sector, chunk_sects)); + + if (sectors < bio_sectors(raid_bio)) { + split = bio_split(raid_bio, sectors, GFP_NOIO, fs_bio_set); + bio_chain(split, raid_bio); + } else + split = raid_bio; + + if (!__chunk_aligned_read(mddev, split)) { + if (split != raid_bio) + generic_make_request(raid_bio); + return split; + } + } while (split != raid_bio); + + return NULL; +} + /* __get_priority_stripe - get the next stripe to process * * Full stripe writes are allowed to pass preread active stripes up until
@@ -5071,7 +5100,7 @@ static void make_request(struct mddev *mddev, struct bio * bi) */ if (rw == READ && mddev->degraded == 0 && mddev->reshape_position == MaxSector && - chunk_aligned_read(mddev,bi)) + (!(bi = chunk_aligned_read(mddev, bi)))) return; if (unlikely(bi->bi_rw & REQ_DISCARD)) {