6.17-stable review patch. If anyone has any objections, please let me know.
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From: Yu Kuai yukuai3@huawei.com
[ Upstream commit b2f5974079d82a4761f002e80601064d4e39a81f ]
Currently, split bio will be chained to original bio, and original bio will be resubmitted to the tail of current->bio_list, waiting for split bio to be issued. However, if split bio get split again, the IO order will be messed up. This problem, on the one hand, will cause performance degradation, especially for mdraid with large IO size; on the other hand, will cause write errors for zoned block devices[1].
For example, in raid456 IO will first be split by max_sector from md_submit_bio(), and then later be split again by chunksize for internal handling:
For example, assume max_sectors is 1M, and chunksize is 512k
1) issue a 2M IO:
bio issuing: 0+2M current->bio_list: NULL
2) md_submit_bio() split by max_sector:
bio issuing: 0+1M current->bio_list: 1M+1M
3) chunk_aligned_read() split by chunksize:
bio issuing: 0+512k current->bio_list: 1M+1M -> 512k+512k
4) after first bio issued, __submit_bio_noacct() will contuine issuing next bio:
bio issuing: 1M+1M current->bio_list: 512k+512k bio issued: 0+512k
5) chunk_aligned_read() split by chunksize:
bio issuing: 1M+512k current->bio_list: 512k+512k -> 1536k+512k bio issued: 0+512k
6) no split afterwards, finally the issue order is:
0+512k -> 1M+512k -> 512k+512k -> 1536k+512k
This behaviour will cause large IO read on raid456 endup to be small discontinuous IO in underlying disks. Fix this problem by placing split bio to the head of current->bio_list.
Test script: test on 8 disk raid5 with 64k chunksize dd if=/dev/md0 of=/dev/null bs=4480k iflag=direct
Test results: Before this patch 1) iostat results: Device r/s rMB/s rrqm/s %rrqm r_await rareq-sz aqu-sz %util md0 52430.00 3276.87 0.00 0.00 0.62 64.00 32.60 80.10 sd* 4487.00 409.00 2054.00 31.40 0.82 93.34 3.68 71.20 2) blktrace G stage: 8,0 0 486445 11.357392936 843 G R 14071424 + 128 [dd] 8,0 0 486451 11.357466360 843 G R 14071168 + 128 [dd] 8,0 0 486454 11.357515868 843 G R 14071296 + 128 [dd] 8,0 0 486468 11.357968099 843 G R 14072192 + 128 [dd] 8,0 0 486474 11.358031320 843 G R 14071936 + 128 [dd] 8,0 0 486480 11.358096298 843 G R 14071552 + 128 [dd] 8,0 0 486490 11.358303858 843 G R 14071808 + 128 [dd] 3) io seek for sdx: Noted io seek is the result from blktrace D stage, statistic of: ABS((offset of next IO) - (offset + len of previous IO))
Read|Write seek cnt 55175, zero cnt 25079 >=(KB) .. <(KB) : count ratio |distribution | 0 .. 1 : 25079 45.5% |########################################| 1 .. 2 : 0 0.0% | | 2 .. 4 : 0 0.0% | | 4 .. 8 : 0 0.0% | | 8 .. 16 : 0 0.0% | | 16 .. 32 : 0 0.0% | | 32 .. 64 : 12540 22.7% |##################### | 64 .. 128 : 2508 4.5% |##### | 128 .. 256 : 0 0.0% | | 256 .. 512 : 10032 18.2% |################# | 512 .. 1024 : 5016 9.1% |######### |
After this patch: 1) iostat results: Device r/s rMB/s rrqm/s %rrqm r_await rareq-sz aqu-sz %util md0 87965.00 5271.88 0.00 0.00 0.16 61.37 14.03 90.60 sd* 6020.00 658.44 5117.00 45.95 0.44 112.00 2.68 86.50 2) blktrace G stage: 8,0 0 206296 5.354894072 664 G R 7156992 + 128 [dd] 8,0 0 206305 5.355018179 664 G R 7157248 + 128 [dd] 8,0 0 206316 5.355204438 664 G R 7157504 + 128 [dd] 8,0 0 206319 5.355241048 664 G R 7157760 + 128 [dd] 8,0 0 206333 5.355500923 664 G R 7158016 + 128 [dd] 8,0 0 206344 5.355837806 664 G R 7158272 + 128 [dd] 8,0 0 206353 5.355960395 664 G R 7158528 + 128 [dd] 8,0 0 206357 5.356020772 664 G R 7158784 + 128 [dd] 3) io seek for sdx Read|Write seek cnt 28644, zero cnt 21483 >=(KB) .. <(KB) : count ratio |distribution | 0 .. 1 : 21483 75.0% |########################################| 1 .. 2 : 0 0.0% | | 2 .. 4 : 0 0.0% | | 4 .. 8 : 0 0.0% | | 8 .. 16 : 0 0.0% | | 16 .. 32 : 0 0.0% | | 32 .. 64 : 7161 25.0% |############## |
BTW, this looks like a long term problem from day one, and large sequential IO read is pretty common case like video playing.
And even with this patch, in this test case IO is merged to at most 128k is due to block layer plug limit BLK_PLUG_FLUSH_SIZE, increase such limit can get even better performance. However, we'll figure out how to do this properly later.
[1] https://lore.kernel.org/all/e40b076d-583d-406b-b223-005910a9f46f@acm.org/
Fixes: d89d87965dcb ("When stacked block devices are in-use (e.g. md or dm), the recursive calls") Reported-by: Tie Ren tieren@fnnas.com Closes: https://lore.kernel.org/all/7dro5o7u5t64d6bgiansesjavxcuvkq5p2pok7dtwkav7b7a... Signed-off-by: Yu Kuai yukuai3@huawei.com Reviewed-by: Bart Van Assche bvanassche@acm.org Reviewed-by: Christoph Hellwig hch@lst.de Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/blk-core.c | 16 ++++++++++------ block/blk-merge.c | 2 +- block/blk-throttle.c | 2 +- block/blk.h | 2 +- 4 files changed, 13 insertions(+), 9 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c index 03a5d4c9cbf72..14ae73eebe0d7 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -727,7 +727,7 @@ static void __submit_bio_noacct_mq(struct bio *bio) current->bio_list = NULL; }
-void submit_bio_noacct_nocheck(struct bio *bio) +void submit_bio_noacct_nocheck(struct bio *bio, bool split) { blk_cgroup_bio_start(bio);
@@ -746,12 +746,16 @@ void submit_bio_noacct_nocheck(struct bio *bio) * to collect a list of requests submited by a ->submit_bio method while * it is active, and then process them after it returned. */ - if (current->bio_list) - bio_list_add(¤t->bio_list[0], bio); - else if (!bdev_test_flag(bio->bi_bdev, BD_HAS_SUBMIT_BIO)) + if (current->bio_list) { + if (split) + bio_list_add_head(¤t->bio_list[0], bio); + else + bio_list_add(¤t->bio_list[0], bio); + } else if (!bdev_test_flag(bio->bi_bdev, BD_HAS_SUBMIT_BIO)) { __submit_bio_noacct_mq(bio); - else + } else { __submit_bio_noacct(bio); + } }
static blk_status_t blk_validate_atomic_write_op_size(struct request_queue *q, @@ -872,7 +876,7 @@ void submit_bio_noacct(struct bio *bio)
if (blk_throtl_bio(bio)) return; - submit_bio_noacct_nocheck(bio); + submit_bio_noacct_nocheck(bio, false); return;
not_supported: diff --git a/block/blk-merge.c b/block/blk-merge.c index c411045fcf03a..77488f11a9441 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -134,7 +134,7 @@ struct bio *bio_submit_split_bioset(struct bio *bio, unsigned int split_sectors, if (should_fail_bio(bio)) bio_io_error(bio); else if (!blk_throtl_bio(bio)) - submit_bio_noacct_nocheck(bio); + submit_bio_noacct_nocheck(bio, true);
return split; } diff --git a/block/blk-throttle.c b/block/blk-throttle.c index cfa1cd60d2c5f..f510ae072868c 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -1224,7 +1224,7 @@ static void blk_throtl_dispatch_work_fn(struct work_struct *work) if (!bio_list_empty(&bio_list_on_stack)) { blk_start_plug(&plug); while ((bio = bio_list_pop(&bio_list_on_stack))) - submit_bio_noacct_nocheck(bio); + submit_bio_noacct_nocheck(bio, false); blk_finish_plug(&plug); } } diff --git a/block/blk.h b/block/blk.h index 18cc3c2afdd4d..d9efc8693aa48 100644 --- a/block/blk.h +++ b/block/blk.h @@ -54,7 +54,7 @@ bool blk_queue_start_drain(struct request_queue *q); bool __blk_freeze_queue_start(struct request_queue *q, struct task_struct *owner); int __bio_queue_enter(struct request_queue *q, struct bio *bio); -void submit_bio_noacct_nocheck(struct bio *bio); +void submit_bio_noacct_nocheck(struct bio *bio, bool split); void bio_await_chain(struct bio *bio);
static inline bool blk_try_enter_queue(struct request_queue *q, bool pm)