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authorMike Snitzer <snitzer@redhat.com>2019-01-17 10:48:01 -0500
committerMike Snitzer <snitzer@redhat.com>2019-01-21 11:29:27 -0500
commita1e1cb72d96491277ede8d257ce6b48a381dd336 (patch)
treeff2a07cc9bbff5a199369f4328978cfd24e4e962 /drivers/md/dm.c
parent57c36519e4b949f89381053f7283f5d605595b42 (diff)
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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>
Diffstat (limited to 'drivers/md/dm.c')
-rw-r--r--drivers/md/dm.c16
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;