blk-throttle: cap discard request size

discard request usually is very big and easily use all bandwidth budget
of a cgroup. discard request size doesn't really mean the size of data
written, so it doesn't make sense to account it into bandwidth budget.
Jens pointed out treating the size 0 doesn't make sense too, because
discard request does have cost. But it's not easy to find the actual
cost. This patch simply makes the size one sector.

Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 14 insertions, 4 deletions

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index a7285bf2831c..80f5481fe9f6 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -382,6 +382,14 @@ static unsigned int tg_iops_limit(struct throtl_grp *tg, int rw)
         }                                                               \
 } while (0)
 
+static inline unsigned int throtl_bio_data_size(struct bio *bio)
+{
+        /* assume it's one sector */
+        if (unlikely(bio_op(bio) == REQ_OP_DISCARD))
+                return 512;
+        return bio->bi_iter.bi_size;
+}
+
 static void throtl_qnode_init(struct throtl_qnode *qn, struct throtl_grp *tg)
 {
         INIT_LIST_HEAD(&qn->node);
@@ -934,6 +942,7 @@ static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
         bool rw = bio_data_dir(bio);
         u64 bytes_allowed, extra_bytes, tmp;
         unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
+        unsigned int bio_size = throtl_bio_data_size(bio);
 
         jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
 
@@ -947,14 +956,14 @@ static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
         do_div(tmp, HZ);
         bytes_allowed = tmp;
 
-        if (tg->bytes_disp[rw] + bio->bi_iter.bi_size <= bytes_allowed) {
+        if (tg->bytes_disp[rw] + bio_size <= bytes_allowed) {
                 if (wait)
                         *wait = 0;
                 return true;
         }
 
         /* Calc approx time to dispatch */
-        extra_bytes = tg->bytes_disp[rw] + bio->bi_iter.bi_size - bytes_allowed;
+        extra_bytes = tg->bytes_disp[rw] + bio_size - bytes_allowed;
         jiffy_wait = div64_u64(extra_bytes * HZ, tg_bps_limit(tg, rw));
 
         if (!jiffy_wait)
@@ -1034,11 +1043,12 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
 static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
 {
         bool rw = bio_data_dir(bio);
+        unsigned int bio_size = throtl_bio_data_size(bio);
 
         /* Charge the bio to the group */
-        tg->bytes_disp[rw] += bio->bi_iter.bi_size;
+        tg->bytes_disp[rw] += bio_size;
         tg->io_disp[rw]++;
-        tg->last_bytes_disp[rw] += bio->bi_iter.bi_size;
+        tg->last_bytes_disp[rw] += bio_size;
         tg->last_io_disp[rw]++;
 
         /*