Hi Tejun,
Could you please kindly review this patch or give some advice?
Thanks.
Jiufei Xue
On 2018/1/23 上午10:08, xuejiufei wrote:
> Cgroup writeback is supported since v4.2. But there exists a problem
> in the following case.
>
> A cgroup may send both buffer and direct/sync IOs. The foreground
> thread will be stalled when periodic writeback IOs is flushed because
> the service queue in block throttle layer already has a plenty of
> writeback IOs, then foreground IOs should be enqueued with its FIFO
> policy. The current policy is dispatching 6 reads and 2 writes during
> each round, sync writes will be significantly delayed.
>
> This patch adds another queue in block throttle. Now there are 3 queues
> in a service queue: read, sync write, async write, and we can dispatch
> more sync writes than aync writes.
>
> Test:
> 1) setup a memcg and a blkcg with uplimit bandwidth 20m/s;
> 2) start a script writing 5G buffer to page cache and start to sync
> 3) start sync writes:
> dd if=/dev/zero of=test bs=4k count=12800 oflag=direct conv=notrunc
>
> Unpatched:
> 52428800 bytes (52 MB) copied, 307.065 s, 171 kB/s
>
> Patched:
> 52428800 bytes (52 MB) copied, 13.8192 s, 3.8 MB/s
>
> Signed-off-by: Jiufei Xue <jiufei.xjf@xxxxxxxxxxxxxxx>
> ---
> block/blk-throttle.c | 195 ++++++++++++++++++++++++++++++++++-----------------
> 1 file changed, 129 insertions(+), 66 deletions(-)
>
> diff --git a/block/blk-throttle.c b/block/blk-throttle.c
> index d19f416..842257e 100644
> --- a/block/blk-throttle.c
> +++ b/block/blk-throttle.c
> @@ -14,10 +14,10 @@
> #include "blk.h"
>
> /* Max dispatch from a group in 1 round */
> -static int throtl_grp_quantum = 8;
> +static int throtl_grp_quantum = 32;
>
> /* Total max dispatch from all groups in one round */
> -static int throtl_quantum = 32;
> +static int throtl_quantum = 128;
>
> /* Throttling is performed over a slice and after that slice is renewed */
> #define DFL_THROTL_SLICE_HD (HZ / 10)
> @@ -43,6 +43,12 @@
> /* A workqueue to queue throttle related work */
> static struct workqueue_struct *kthrotld_workqueue;
>
> +enum wl_type {
> + READ_WORKLOAD = 0,
> + SYNC_WRITE_WORKLOAD = 1,
> + ASYNC_WRITE_WORKLOAD = 2
> +};
> +
> /*
> * To implement hierarchical throttling, throtl_grps form a tree and bios
> * are dispatched upwards level by level until they reach the top and get
> @@ -79,8 +85,11 @@ struct throtl_service_queue {
> * Bios queued directly to this service_queue or dispatched from
> * children throtl_grp's.
> */
> - struct list_head queued[2]; /* throtl_qnode [READ/WRITE] */
> - unsigned int nr_queued[2]; /* number of queued bios */
> + /* throtl_qnode [READ/WRITE/ASYNC_WRITE] */
> + struct list_head queued[3];
> +
> + unsigned int nr_queued[3]; /* number of queued bios */
> +
>
> /*
> * RB tree of active children throtl_grp's, which are sorted by
> @@ -127,8 +136,8 @@ struct throtl_grp {
> * with the sibling qnode_on_parents and the parent's
> * qnode_on_self.
> */
> - struct throtl_qnode qnode_on_self[2];
> - struct throtl_qnode qnode_on_parent[2];
> + struct throtl_qnode qnode_on_self[3];
> + struct throtl_qnode qnode_on_parent[3];
>
> /*
> * Dispatch time in jiffies. This is the estimated time when group
> @@ -202,7 +211,7 @@ struct throtl_data
> struct request_queue *queue;
>
> /* Total Number of queued bios on READ and WRITE lists */
> - unsigned int nr_queued[2];
> + unsigned int nr_queued[3];
>
> unsigned int throtl_slice;
>
> @@ -274,6 +283,18 @@ static struct throtl_data *sq_to_td(struct throtl_service_queue *sq)
> return container_of(sq, struct throtl_data, service_queue);
> }
>
> +static inline enum wl_type bio_workload_type(struct bio *bio)
> +{
> + return bio_data_dir(bio) ?
> + ((bio->bi_opf & REQ_SYNC) ? SYNC_WRITE_WORKLOAD :
> + ASYNC_WRITE_WORKLOAD) : READ_WORKLOAD;
> +}
> +
> +static inline bool wl_to_rw(enum wl_type type)
> +{
> + return type >= SYNC_WRITE_WORKLOAD;
> +}
> +
> /*
> * cgroup's limit in LIMIT_MAX is scaled if low limit is set. This scale is to
> * make the IO dispatch more smooth.
> @@ -475,8 +496,9 @@ static struct bio *throtl_pop_queued(struct list_head *queued,
> /* init a service_queue, assumes the caller zeroed it */
> static void throtl_service_queue_init(struct throtl_service_queue *sq)
> {
> - INIT_LIST_HEAD(&sq->queued[0]);
> - INIT_LIST_HEAD(&sq->queued[1]);
> + INIT_LIST_HEAD(&sq->queued[READ_WORKLOAD]);
> + INIT_LIST_HEAD(&sq->queued[SYNC_WRITE_WORKLOAD]);
> + INIT_LIST_HEAD(&sq->queued[ASYNC_WRITE_WORKLOAD]);
> sq->pending_tree = RB_ROOT;
> timer_setup(&sq->pending_timer, throtl_pending_timer_fn, 0);
> }
> @@ -484,7 +506,7 @@ static void throtl_service_queue_init(struct throtl_service_queue *sq)
> static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)
> {
> struct throtl_grp *tg;
> - int rw;
> + enum wl_type type;
>
> tg = kzalloc_node(sizeof(*tg), gfp, node);
> if (!tg)
> @@ -492,9 +514,9 @@ static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)
>
> throtl_service_queue_init(&tg->service_queue);
>
> - for (rw = READ; rw <= WRITE; rw++) {
> - throtl_qnode_init(&tg->qnode_on_self[rw], tg);
> - throtl_qnode_init(&tg->qnode_on_parent[rw], tg);
> + for (type = READ_WORKLOAD; type <= ASYNC_WRITE_WORKLOAD; type++) {
> + throtl_qnode_init(&tg->qnode_on_self[type], tg);
> + throtl_qnode_init(&tg->qnode_on_parent[type], tg);
> }
>
> RB_CLEAR_NODE(&tg->rb_node);
> @@ -985,6 +1007,7 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
> unsigned long *wait)
> {
> bool rw = bio_data_dir(bio);
> + enum wl_type type = bio_workload_type(bio);
> unsigned long bps_wait = 0, iops_wait = 0, max_wait = 0;
>
> /*
> @@ -993,8 +1016,8 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
> * this function with a different bio if there are other bios
> * queued.
> */
> - BUG_ON(tg->service_queue.nr_queued[rw] &&
> - bio != throtl_peek_queued(&tg->service_queue.queued[rw]));
> + BUG_ON(tg->service_queue.nr_queued[type] &&
> + bio != throtl_peek_queued(&tg->service_queue.queued[type]));
>
> /* If tg->bps = -1, then BW is unlimited */
> if (tg_bps_limit(tg, rw) == U64_MAX &&
> @@ -1011,7 +1034,12 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
> * If there is queued bio, that means there should be an active
> * slice and it should be extended instead.
> */
> - if (throtl_slice_used(tg, rw) && !(tg->service_queue.nr_queued[rw]))
> + if (throtl_slice_used(tg, rw) &&
> + ((rw == READ &&
> + !tg->service_queue.nr_queued[READ_WORKLOAD]) ||
> + (rw == WRITE &&
> + !tg->service_queue.nr_queued[SYNC_WRITE_WORKLOAD] &&
> + !tg->service_queue.nr_queued[ASYNC_WRITE_WORKLOAD])))
> throtl_start_new_slice(tg, rw);
> else {
> if (time_before(tg->slice_end[rw],
> @@ -1072,10 +1100,10 @@ static void throtl_add_bio_tg(struct bio *bio, struct throtl_qnode *qn,
> struct throtl_grp *tg)
> {
> struct throtl_service_queue *sq = &tg->service_queue;
> - bool rw = bio_data_dir(bio);
> + int type = bio_workload_type(bio);
>
> if (!qn)
> - qn = &tg->qnode_on_self[rw];
> + qn = &tg->qnode_on_self[type];
>
> /*
> * If @tg doesn't currently have any bios queued in the same
> @@ -1083,12 +1111,12 @@ static void throtl_add_bio_tg(struct bio *bio, struct throtl_qnode *qn,
> * dispatched. Mark that @tg was empty. This is automatically
> * cleaered on the next tg_update_disptime().
> */
> - if (!sq->nr_queued[rw])
> + if (!sq->nr_queued[type])
> tg->flags |= THROTL_TG_WAS_EMPTY;
>
> - throtl_qnode_add_bio(bio, qn, &sq->queued[rw]);
> + throtl_qnode_add_bio(bio, qn, &sq->queued[type]);
>
> - sq->nr_queued[rw]++;
> + sq->nr_queued[type]++;
> throtl_enqueue_tg(tg);
> }
>
> @@ -1096,16 +1124,22 @@ static void tg_update_disptime(struct throtl_grp *tg)
> {
> struct throtl_service_queue *sq = &tg->service_queue;
> unsigned long read_wait = -1, write_wait = -1, min_wait = -1, disptime;
> + unsigned long sync_write_wait, async_write_wait;
> struct bio *bio;
>
> - bio = throtl_peek_queued(&sq->queued[READ]);
> + bio = throtl_peek_queued(&sq->queued[READ_WORKLOAD]);
> if (bio)
> tg_may_dispatch(tg, bio, &read_wait);
>
> - bio = throtl_peek_queued(&sq->queued[WRITE]);
> + bio = throtl_peek_queued(&sq->queued[SYNC_WRITE_WORKLOAD]);
> + if (bio)
> + tg_may_dispatch(tg, bio, &sync_write_wait);
> +
> + bio = throtl_peek_queued(&sq->queued[ASYNC_WRITE_WORKLOAD]);
> if (bio)
> - tg_may_dispatch(tg, bio, &write_wait);
> + tg_may_dispatch(tg, bio, &async_write_wait);
>
> + write_wait = min(sync_write_wait, async_write_wait);
> min_wait = min(read_wait, write_wait);
> disptime = jiffies + min_wait;
>
> @@ -1125,16 +1159,16 @@ static void start_parent_slice_with_credit(struct throtl_grp *child_tg,
> throtl_start_new_slice_with_credit(parent_tg, rw,
> child_tg->slice_start[rw]);
> }
> -
> }
>
> -static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
> +static void tg_dispatch_one_bio(struct throtl_grp *tg, enum wl_type type)
> {
> struct throtl_service_queue *sq = &tg->service_queue;
> struct throtl_service_queue *parent_sq = sq->parent_sq;
> struct throtl_grp *parent_tg = sq_to_tg(parent_sq);
> struct throtl_grp *tg_to_put = NULL;
> struct bio *bio;
> + bool rw = wl_to_rw(type);
>
> /*
> * @bio is being transferred from @tg to @parent_sq. Popping a bio
> @@ -1142,8 +1176,8 @@ static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
> * getting released prematurely. Remember the tg to put and put it
> * after @bio is transferred to @parent_sq.
> */
> - bio = throtl_pop_queued(&sq->queued[rw], &tg_to_put);
> - sq->nr_queued[rw]--;
> + bio = throtl_pop_queued(&sq->queued[type], &tg_to_put);
> + sq->nr_queued[type]--;
>
> throtl_charge_bio(tg, bio);
>
> @@ -1155,13 +1189,13 @@ static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
> * responsible for issuing these bios.
> */
> if (parent_tg) {
> - throtl_add_bio_tg(bio, &tg->qnode_on_parent[rw], parent_tg);
> + throtl_add_bio_tg(bio, &tg->qnode_on_parent[type], parent_tg);
> start_parent_slice_with_credit(tg, parent_tg, rw);
> } else {
> - throtl_qnode_add_bio(bio, &tg->qnode_on_parent[rw],
> - &parent_sq->queued[rw]);
> - BUG_ON(tg->td->nr_queued[rw] <= 0);
> - tg->td->nr_queued[rw]--;
> + throtl_qnode_add_bio(bio, &tg->qnode_on_parent[type],
> + &parent_sq->queued[type]);
> + BUG_ON(tg->td->nr_queued[type] <= 0);
> + tg->td->nr_queued[type]--;
> }
>
> throtl_trim_slice(tg, rw);
> @@ -1173,34 +1207,45 @@ static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
> static int throtl_dispatch_tg(struct throtl_grp *tg)
> {
> struct throtl_service_queue *sq = &tg->service_queue;
> - unsigned int nr_reads = 0, nr_writes = 0;
> + unsigned int nr_reads = 0, nr_async_writes = 0, nr_sync_writes = 0;
> unsigned int max_nr_reads = throtl_grp_quantum*3/4;
> - unsigned int max_nr_writes = throtl_grp_quantum - max_nr_reads;
> + unsigned int max_sync_writes = (throtl_grp_quantum - max_nr_reads)*7/8;
> + unsigned int max_async_writes = throtl_grp_quantum - max_nr_reads
> + - max_sync_writes;
> struct bio *bio;
>
> /* Try to dispatch 75% READS and 25% WRITES */
> -
> - while ((bio = throtl_peek_queued(&sq->queued[READ])) &&
> + while ((bio = throtl_peek_queued(&sq->queued[READ_WORKLOAD])) &&
> tg_may_dispatch(tg, bio, NULL)) {
>
> - tg_dispatch_one_bio(tg, bio_data_dir(bio));
> + tg_dispatch_one_bio(tg, READ_WORKLOAD);
> nr_reads++;
>
> if (nr_reads >= max_nr_reads)
> break;
> }
>
> - while ((bio = throtl_peek_queued(&sq->queued[WRITE])) &&
> + while ((bio = throtl_peek_queued(&sq->queued[SYNC_WRITE_WORKLOAD])) &&
> tg_may_dispatch(tg, bio, NULL)) {
>
> - tg_dispatch_one_bio(tg, bio_data_dir(bio));
> - nr_writes++;
> + tg_dispatch_one_bio(tg, SYNC_WRITE_WORKLOAD);
> + nr_sync_writes++;
>
> - if (nr_writes >= max_nr_writes)
> + if (nr_sync_writes >= max_sync_writes)
> break;
> }
>
> - return nr_reads + nr_writes;
> + while ((bio = throtl_peek_queued(&sq->queued[ASYNC_WRITE_WORKLOAD])) &&
> + tg_may_dispatch(tg, bio, NULL)) {
> +
> + tg_dispatch_one_bio(tg, ASYNC_WRITE_WORKLOAD);
> + nr_async_writes++;
> +
> + if (nr_async_writes >= max_async_writes)
> + break;
> + }
> +
> + return nr_reads + nr_sync_writes + nr_async_writes;
> }
>
> static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
> @@ -1221,7 +1266,9 @@ static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
>
> nr_disp += throtl_dispatch_tg(tg);
>
> - if (sq->nr_queued[0] || sq->nr_queued[1])
> + if (sq->nr_queued[READ_WORKLOAD] ||
> + sq->nr_queued[SYNC_WRITE_WORKLOAD] ||
> + sq->nr_queued[ASYNC_WRITE_WORKLOAD])
> tg_update_disptime(tg);
>
> if (nr_disp >= throtl_quantum)
> @@ -1267,9 +1314,14 @@ static void throtl_pending_timer_fn(struct timer_list *t)
> dispatched = false;
>
> while (true) {
> - throtl_log(sq, "dispatch nr_queued=%u read=%u write=%u",
> - sq->nr_queued[READ] + sq->nr_queued[WRITE],
> - sq->nr_queued[READ], sq->nr_queued[WRITE]);
> + throtl_log(sq,
> + "dispatch nr_queued=%u read=%u sync_write=%u async_write=%u",
> + sq->nr_queued[READ_WORKLOAD] +
> + sq->nr_queued[SYNC_WRITE_WORKLOAD] +
> + sq->nr_queued[ASYNC_WRITE_WORKLOAD],
> + sq->nr_queued[READ_WORKLOAD],
> + sq->nr_queued[SYNC_WRITE_WORKLOAD],
> + sq->nr_queued[ASYNC_WRITE_WORKLOAD]);
>
> ret = throtl_select_dispatch(sq);
> if (ret) {
> @@ -1325,13 +1377,13 @@ static void blk_throtl_dispatch_work_fn(struct work_struct *work)
> struct bio_list bio_list_on_stack;
> struct bio *bio;
> struct blk_plug plug;
> - int rw;
> + enum wl_type type;
>
> bio_list_init(&bio_list_on_stack);
>
> spin_lock_irq(q->queue_lock);
> - for (rw = READ; rw <= WRITE; rw++)
> - while ((bio = throtl_pop_queued(&td_sq->queued[rw], NULL)))
> + for (type = READ_WORKLOAD; type <= ASYNC_WRITE_WORKLOAD; type++)
> + while ((bio = throtl_pop_queued(&td_sq->queued[type], NULL)))
> bio_list_add(&bio_list_on_stack, bio);
> spin_unlock_irq(q->queue_lock);
>
> @@ -1820,11 +1872,13 @@ static bool throtl_tg_can_upgrade(struct throtl_grp *tg)
> write_limit = tg->bps[WRITE][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW];
> if (!read_limit && !write_limit)
> return true;
> - if (read_limit && sq->nr_queued[READ] &&
> - (!write_limit || sq->nr_queued[WRITE]))
> + if (read_limit && sq->nr_queued[READ_WORKLOAD] &&
> + (!write_limit || sq->nr_queued[SYNC_WRITE_WORKLOAD] ||
> + sq->nr_queued[ASYNC_WRITE_WORKLOAD]))
> return true;
> - if (write_limit && sq->nr_queued[WRITE] &&
> - (!read_limit || sq->nr_queued[READ]))
> + if (write_limit && (sq->nr_queued[SYNC_WRITE_WORKLOAD] ||
> + sq->nr_queued[ASYNC_WRITE_WORKLOAD]) &&
> + (!read_limit || sq->nr_queued[READ_WORKLOAD]))
> return true;
>
> if (time_after_eq(jiffies,
> @@ -2129,6 +2183,7 @@ bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
> struct throtl_grp *tg = blkg_to_tg(blkg ?: q->root_blkg);
> struct throtl_service_queue *sq;
> bool rw = bio_data_dir(bio);
> + enum wl_type type = bio_workload_type(bio);
> bool throttled = false;
> struct throtl_data *td = tg->td;
>
> @@ -2157,7 +2212,7 @@ bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
> throtl_downgrade_check(tg);
> throtl_upgrade_check(tg);
> /* throtl is FIFO - if bios are already queued, should queue */
> - if (sq->nr_queued[rw])
> + if (sq->nr_queued[type])
> break;
>
> /* if above limits, break to queue */
> @@ -2191,7 +2246,7 @@ bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
> * Climb up the ladder. If we''re already at the top, it
> * can be executed directly.
> */
> - qn = &tg->qnode_on_parent[rw];
> + qn = &tg->qnode_on_parent[type];
> sq = sq->parent_sq;
> tg = sq_to_tg(sq);
> if (!tg)
> @@ -2199,16 +2254,19 @@ bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
> }
>
> /* out-of-limit, queue to @tg */
> - throtl_log(sq, "[%c] bio. bdisp=%llu sz=%u bps=%llu iodisp=%u iops=%u queued=%d/%d",
> + throtl_log(sq, "[%c] bio. bdisp=%llu sz=%u bps=%llu iodisp=%u "
> + "iops=%u queued=%d/%d/%d",
> rw == READ ? 'R' : 'W',
> tg->bytes_disp[rw], bio->bi_iter.bi_size,
> tg_bps_limit(tg, rw),
> tg->io_disp[rw], tg_iops_limit(tg, rw),
> - sq->nr_queued[READ], sq->nr_queued[WRITE]);
> + sq->nr_queued[READ_WORKLOAD],
> + sq->nr_queued[SYNC_WRITE_WORKLOAD],
> + sq->nr_queued[ASYNC_WRITE_WORKLOAD]);
>
> tg->last_low_overflow_time[rw] = jiffies;
>
> - td->nr_queued[rw]++;
> + td->nr_queued[type]++;
> throtl_add_bio_tg(bio, qn, tg);
> throttled = true;
>
> @@ -2334,10 +2392,15 @@ static void tg_drain_bios(struct throtl_service_queue *parent_sq)
>
> throtl_dequeue_tg(tg);
>
> - while ((bio = throtl_peek_queued(&sq->queued[READ])))
> - tg_dispatch_one_bio(tg, bio_data_dir(bio));
> - while ((bio = throtl_peek_queued(&sq->queued[WRITE])))
> - tg_dispatch_one_bio(tg, bio_data_dir(bio));
> + while ((bio =
> + throtl_peek_queued(&sq->queued[READ_WORKLOAD])))
> + tg_dispatch_one_bio(tg, READ_WORKLOAD);
> + while ((bio =
> + throtl_peek_queued(&sq->queued[SYNC_WRITE_WORKLOAD])))
> + tg_dispatch_one_bio(tg, SYNC_WRITE_WORKLOAD);
> + while ((bio =
> + throtl_peek_queued(&sq->queued[ASYNC_WRITE_WORKLOAD])))
> + tg_dispatch_one_bio(tg, ASYNC_WRITE_WORKLOAD);
> }
> }
>
> @@ -2354,7 +2417,7 @@ void blk_throtl_drain(struct request_queue *q)
> struct blkcg_gq *blkg;
> struct cgroup_subsys_state *pos_css;
> struct bio *bio;
> - int rw;
> + enum wl_type type;
>
> queue_lockdep_assert_held(q);
> rcu_read_lock();
> @@ -2375,8 +2438,8 @@ void blk_throtl_drain(struct request_queue *q)
> spin_unlock_irq(q->queue_lock);
>
> /* all bios now should be in td->service_queue, issue them */
> - for (rw = READ; rw <= WRITE; rw++)
> - while ((bio = throtl_pop_queued(&td->service_queue.queued[rw],
> + for (type = READ_WORKLOAD; type <= ASYNC_WRITE_WORKLOAD; type++)
> + while ((bio = throtl_pop_queued(&td->service_queue.queued[type],
> NULL)))
> generic_make_request(bio);
>
>
