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blk-throttle: fix that io throttle can only work for single bio

Browse Source 
Test scripts:
cd /sys/fs/cgroup/blkio/
echo "8:0 1024" > blkio.throttle.write_bps_device
echo $$ > cgroup.procs
dd if=/dev/zero of=/dev/sda bs=10k count=1 oflag=direct &
dd if=/dev/zero of=/dev/sda bs=10k count=1 oflag=direct &

Test result:
10240 bytes (10 kB, 10 KiB) copied, 10.0134 s, 1.0 kB/s
10240 bytes (10 kB, 10 KiB) copied, 10.0135 s, 1.0 kB/s

The problem is that the second bio is finished after 10s instead of 20s.

Root cause:
1) second bio will be flagged:

__blk_throtl_bio
 while (true) {
  ...
  if (sq->nr_queued[rw]) -> some bio is throttled already
   break
 };
 bio_set_flag(bio, BIO_THROTTLED); -> flag the bio

2) flagged bio will be dispatched without waiting:

throtl_dispatch_tg
 tg_may_dispatch
  tg_with_in_bps_limit
   if (bps_limit == U64_MAX || bio_flagged(bio, BIO_THROTTLED))
    *wait = 0; -> wait time is zero
    return true;

commit 9f5ede3c01 ("block: throttle split bio in case of iops limit")
support to count split bios for iops limit, thus it adds flagged bio
checking in tg_with_in_bps_limit() so that split bios will only count
once for bps limit, however, it introduce a new problem that io throttle
won't work if multiple bios are throttled.

In order to fix the problem, handle iops/bps limit in different ways:

1) for iops limit, there is no flag to record if the bio is throttled,
   and iops is always applied.
2) for bps limit, original bio will be flagged with BIO_BPS_THROTTLED,
   and io throttle will ignore bio with the flag.

Noted this patch also remove the code to set flag in __bio_clone(), it's
introduced in commit 111be88398 ("block-throttle: avoid double
charge"), and author thinks split bio can be resubmited and throttled
again, which is wrong because split bio will continue to dispatch from
caller.

Fixes: 9f5ede3c01 ("block: throttle split bio in case of iops limit")
Cc: <stable@vger.kernel.org>
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20220829022240.3348319-2-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Yu Kuai 2022-08-29 10:22:37 +08:00 committed by Jens Axboe
parent 4acb83417c
commit 320fb0f91e
5 changed files with 9 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
block/bio.c
View File

@ -760,8 +760,6 @@ EXPORT_SYMBOL(bio_put);
static int __bio_clone(struct bio *bio, struct bio *bio_src, gfp_t gfp)
{
bio_set_flag(bio, BIO_CLONED);
if (bio_flagged(bio_src, BIO_THROTTLED))
bio_set_flag(bio, BIO_THROTTLED);
bio->bi_ioprio = bio_src->bi_ioprio;
bio->bi_iter = bio_src->bi_iter;

20
block/blk-throttle.c
View File

@ -811,7 +811,7 @@ static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
unsigned int bio_size = throtl_bio_data_size(bio);
/* no need to throttle if this bio's bytes have been accounted */
if (bps_limit == U64_MAX || bio_flagged(bio, BIO_THROTTLED)) {
if (bps_limit == U64_MAX || bio_flagged(bio, BIO_BPS_THROTTLED)) {
if (wait)
*wait = 0;
return true;
@ -921,22 +921,13 @@ static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
unsigned int bio_size = throtl_bio_data_size(bio);
/* Charge the bio to the group */
if (!bio_flagged(bio, BIO_THROTTLED)) {
if (!bio_flagged(bio, BIO_BPS_THROTTLED)) {
tg->bytes_disp[rw] += bio_size;
tg->last_bytes_disp[rw] += bio_size;
}
tg->io_disp[rw]++;
tg->last_io_disp[rw]++;
/*
* BIO_THROTTLED is used to prevent the same bio to be throttled
* more than once as a throttled bio will go through blk-throtl the
* second time when it eventually gets issued. Set it when a bio
* is being charged to a tg.
*/
if (!bio_flagged(bio, BIO_THROTTLED))
bio_set_flag(bio, BIO_THROTTLED);
}
/**
@ -1026,6 +1017,7 @@ static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
sq->nr_queued[rw]--;
throtl_charge_bio(tg, bio);
bio_set_flag(bio, BIO_BPS_THROTTLED);
/*
* If our parent is another tg, we just need to transfer @bio to
@ -2181,8 +2173,10 @@ again:
qn = &tg->qnode_on_parent[rw];
sq = sq->parent_sq;
tg = sq_to_tg(sq);
if (!tg)
if (!tg) {
bio_set_flag(bio, BIO_BPS_THROTTLED);
goto out_unlock;
}
}
/* out-of-limit, queue to @tg */
@ -2211,8 +2205,6 @@ again:
}
out_unlock:
bio_set_flag(bio, BIO_THROTTLED);
#ifdef CONFIG_BLK_DEV_THROTTLING_LOW
if (throttled || !td->track_bio_latency)
bio->bi_issue.value |= BIO_ISSUE_THROTL_SKIP_LATENCY;

2
block/blk-throttle.h
View File

@ -175,7 +175,7 @@ static inline bool blk_throtl_bio(struct bio *bio)
struct throtl_grp *tg = blkg_to_tg(bio->bi_blkg);
/* no need to throttle bps any more if the bio has been throttled */
if (bio_flagged(bio, BIO_THROTTLED) &&
if (bio_flagged(bio, BIO_BPS_THROTTLED) &&
!(tg->flags & THROTL_TG_HAS_IOPS_LIMIT))
return false;

2
include/linux/bio.h
View File

@ -509,7 +509,7 @@ static inline void bio_set_dev(struct bio *bio, struct block_device *bdev)
{
bio_clear_flag(bio, BIO_REMAPPED);
if (bio->bi_bdev != bdev)
bio_clear_flag(bio, BIO_THROTTLED);
bio_clear_flag(bio, BIO_BPS_THROTTLED);
bio->bi_bdev = bdev;
bio_associate_blkg(bio);
}

2
include/linux/blk_types.h
View File

@ -325,7 +325,7 @@ enum {
BIO_QUIET, /* Make BIO Quiet */
BIO_CHAIN, /* chained bio, ->bi_remaining in effect */
BIO_REFFED, /* bio has elevated ->bi_cnt */
BIO_THROTTLED, /* This bio has already been subjected to
BIO_BPS_THROTTLED, /* This bio has already been subjected to
* throttling rules. Don't do it again. */
BIO_TRACE_COMPLETION, /* bio_endio() should trace the final completion
* of this bio. */