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author | Mike Snitzer <snitzer@redhat.com> | 2019-01-17 18:48:01 +0300 |
---|---|---|
committer | Mike Snitzer <snitzer@redhat.com> | 2019-01-21 19:29:27 +0300 |
commit | a1e1cb72d96491277ede8d257ce6b48a381dd336 (patch) | |
tree | ff2a07cc9bbff5a199369f4328978cfd24e4e962 | |
parent | 57c36519e4b949f89381053f7283f5d605595b42 (diff) | |
download | linux-a1e1cb72d96491277ede8d257ce6b48a381dd336.tar.xz |
dm: fix redundant IO accounting for bios that need splitting
The risk of redundant IO accounting was not taken into consideration
when commit 18a25da84354 ("dm: ensure bio submission follows a
depth-first tree walk") introduced IO splitting in terms of recursion
via generic_make_request().
Fix this by subtracting the split bio's payload from the IO stats that
were already accounted for by start_io_acct() upon dm_make_request()
entry. This repeat oscillation of the IO accounting, up then down,
isn't ideal but refactoring DM core's IO splitting to pre-split bios
_before_ they are accounted turned out to be an excessive amount of
change that will need a full development cycle to refine and verify.
Before this fix:
/dev/mapper/stripe_dev is a 4-way stripe using a 32k chunksize, so
bios are split on 32k boundaries.
# fio --name=16M --filename=/dev/mapper/stripe_dev --rw=write --bs=64k --size=16M \
--iodepth=1 --ioengine=libaio --direct=1 --refill_buffers
with debugging added:
[103898.310264] device-mapper: core: start_io_acct: dm-2 WRITE bio->bi_iter.bi_sector=0 len=128
[103898.318704] device-mapper: core: __split_and_process_bio: recursing for following split bio:
[103898.329136] device-mapper: core: start_io_acct: dm-2 WRITE bio->bi_iter.bi_sector=64 len=64
...
16M written yet 136M (278528 * 512b) accounted:
# cat /sys/block/dm-2/stat | awk '{ print $7 }'
278528
After this fix:
16M written and 16M (32768 * 512b) accounted:
# cat /sys/block/dm-2/stat | awk '{ print $7 }'
32768
Fixes: 18a25da84354 ("dm: ensure bio submission follows a depth-first tree walk")
Cc: stable@vger.kernel.org # 4.16+
Reported-by: Bryan Gurney <bgurney@redhat.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
-rw-r--r-- | drivers/md/dm.c | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/drivers/md/dm.c b/drivers/md/dm.c index fcb97b0a5743..fbadda68e23b 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -1584,6 +1584,9 @@ static void init_clone_info(struct clone_info *ci, struct mapped_device *md, ci->sector = bio->bi_iter.bi_sector; } +#define __dm_part_stat_sub(part, field, subnd) \ + (part_stat_get(part, field) -= (subnd)) + /* * Entry point to split a bio into clones and submit them to the targets. */ @@ -1638,6 +1641,19 @@ static blk_qc_t __split_and_process_bio(struct mapped_device *md, struct bio *b = bio_split(bio, bio_sectors(bio) - ci.sector_count, GFP_NOIO, &md->queue->bio_split); ci.io->orig_bio = b; + + /* + * Adjust IO stats for each split, otherwise upon queue + * reentry there will be redundant IO accounting. + * NOTE: this is a stop-gap fix, a proper fix involves + * significant refactoring of DM core's bio splitting + * (by eliminating DM's splitting and just using bio_split) + */ + part_stat_lock(); + __dm_part_stat_sub(&dm_disk(md)->part0, + sectors[op_stat_group(bio_op(bio))], ci.sector_count); + part_stat_unlock(); + bio_chain(b, bio); ret = generic_make_request(bio); break; |