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Subject[PATCH 1/8] block: change the request allocation/congestion logic to be sync/async based
Date
This makes sure that we never wait on async IO for sync requests, instead
of doing the split on writes vs reads.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
block/blk-core.c | 70 +++++++++++++++++++++---------------------
block/blk-sysfs.c | 40 ++++++++++++------------
block/elevator.c | 2 +-
include/linux/backing-dev.h | 12 ++++----
include/linux/blkdev.h | 52 +++++++++++++++++++++----------
mm/backing-dev.c | 10 +++---
6 files changed, 102 insertions(+), 84 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index 996ed90..a32b571 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -484,11 +484,11 @@ static int blk_init_free_list(struct request_queue *q)
{
struct request_list *rl = &q->rq;

- rl->count[READ] = rl->count[WRITE] = 0;
- rl->starved[READ] = rl->starved[WRITE] = 0;
+ rl->count[BLK_RW_SYNC] = rl->count[BLK_RW_ASYNC] = 0;
+ rl->starved[BLK_RW_SYNC] = rl->starved[BLK_RW_ASYNC] = 0;
rl->elvpriv = 0;
- init_waitqueue_head(&rl->wait[READ]);
- init_waitqueue_head(&rl->wait[WRITE]);
+ init_waitqueue_head(&rl->wait[BLK_RW_SYNC]);
+ init_waitqueue_head(&rl->wait[BLK_RW_ASYNC]);

rl->rq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
mempool_free_slab, request_cachep, q->node);
@@ -699,18 +699,18 @@ static void ioc_set_batching(struct request_queue *q, struct io_context *ioc)
ioc->last_waited = jiffies;
}

-static void __freed_request(struct request_queue *q, int rw)
+static void __freed_request(struct request_queue *q, int sync)
{
struct request_list *rl = &q->rq;

- if (rl->count[rw] < queue_congestion_off_threshold(q))
- blk_clear_queue_congested(q, rw);
+ if (rl->count[sync] < queue_congestion_off_threshold(q))
+ blk_clear_queue_congested(q, sync);

- if (rl->count[rw] + 1 <= q->nr_requests) {
- if (waitqueue_active(&rl->wait[rw]))
- wake_up(&rl->wait[rw]);
+ if (rl->count[sync] + 1 <= q->nr_requests) {
+ if (waitqueue_active(&rl->wait[sync]))
+ wake_up(&rl->wait[sync]);

- blk_clear_queue_full(q, rw);
+ blk_clear_queue_full(q, sync);
}
}

@@ -718,18 +718,18 @@ static void __freed_request(struct request_queue *q, int rw)
* A request has just been released. Account for it, update the full and
* congestion status, wake up any waiters. Called under q->queue_lock.
*/
-static void freed_request(struct request_queue *q, int rw, int priv)
+static void freed_request(struct request_queue *q, int sync, int priv)
{
struct request_list *rl = &q->rq;

- rl->count[rw]--;
+ rl->count[sync]--;
if (priv)
rl->elvpriv--;

- __freed_request(q, rw);
+ __freed_request(q, sync);

- if (unlikely(rl->starved[rw ^ 1]))
- __freed_request(q, rw ^ 1);
+ if (unlikely(rl->starved[sync ^ 1]))
+ __freed_request(q, sync ^ 1);
}

/*
@@ -743,15 +743,15 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
struct request *rq = NULL;
struct request_list *rl = &q->rq;
struct io_context *ioc = NULL;
- const int rw = rw_flags & 0x01;
+ const bool is_sync = rw_is_sync(rw_flags) != 0;
int may_queue, priv;

may_queue = elv_may_queue(q, rw_flags);
if (may_queue == ELV_MQUEUE_NO)
goto rq_starved;

- if (rl->count[rw]+1 >= queue_congestion_on_threshold(q)) {
- if (rl->count[rw]+1 >= q->nr_requests) {
+ if (rl->count[is_sync]+1 >= queue_congestion_on_threshold(q)) {
+ if (rl->count[is_sync]+1 >= q->nr_requests) {
ioc = current_io_context(GFP_ATOMIC, q->node);
/*
* The queue will fill after this allocation, so set
@@ -759,9 +759,9 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
* This process will be allowed to complete a batch of
* requests, others will be blocked.
*/
- if (!blk_queue_full(q, rw)) {
+ if (!blk_queue_full(q, is_sync)) {
ioc_set_batching(q, ioc);
- blk_set_queue_full(q, rw);
+ blk_set_queue_full(q, is_sync);
} else {
if (may_queue != ELV_MQUEUE_MUST
&& !ioc_batching(q, ioc)) {
@@ -774,7 +774,7 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
}
}
}
- blk_set_queue_congested(q, rw);
+ blk_set_queue_congested(q, is_sync);
}

/*
@@ -782,11 +782,11 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
* limit of requests, otherwise we could have thousands of requests
* allocated with any setting of ->nr_requests
*/
- if (rl->count[rw] >= (3 * q->nr_requests / 2))
+ if (rl->count[is_sync] >= (3 * q->nr_requests / 2))
goto out;

- rl->count[rw]++;
- rl->starved[rw] = 0;
+ rl->count[is_sync]++;
+ rl->starved[is_sync] = 0;

priv = !test_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
if (priv)
@@ -804,7 +804,7 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
* wait queue, but this is pretty rare.
*/
spin_lock_irq(q->queue_lock);
- freed_request(q, rw, priv);
+ freed_request(q, is_sync, priv);

/*
* in the very unlikely event that allocation failed and no
@@ -814,8 +814,8 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
* rq mempool into READ and WRITE
*/
rq_starved:
- if (unlikely(rl->count[rw] == 0))
- rl->starved[rw] = 1;
+ if (unlikely(rl->count[is_sync] == 0))
+ rl->starved[is_sync] = 1;

goto out;
}
@@ -829,7 +829,7 @@ rq_starved:
if (ioc_batching(q, ioc))
ioc->nr_batch_requests--;

- trace_block_getrq(q, bio, rw);
+ trace_block_getrq(q, bio, rw_flags & 1);
out:
return rq;
}
@@ -843,7 +843,7 @@ out:
static struct request *get_request_wait(struct request_queue *q, int rw_flags,
struct bio *bio)
{
- const int rw = rw_flags & 0x01;
+ const bool is_sync = rw_is_sync(rw_flags) != 0;
struct request *rq;

rq = get_request(q, rw_flags, bio, GFP_NOIO);
@@ -852,10 +852,10 @@ static struct request *get_request_wait(struct request_queue *q, int rw_flags,
struct io_context *ioc;
struct request_list *rl = &q->rq;

- prepare_to_wait_exclusive(&rl->wait[rw], &wait,
+ prepare_to_wait_exclusive(&rl->wait[is_sync], &wait,
TASK_UNINTERRUPTIBLE);

- trace_block_sleeprq(q, bio, rw);
+ trace_block_sleeprq(q, bio, rw_flags & 1);

__generic_unplug_device(q);
spin_unlock_irq(q->queue_lock);
@@ -871,7 +871,7 @@ static struct request *get_request_wait(struct request_queue *q, int rw_flags,
ioc_set_batching(q, ioc);

spin_lock_irq(q->queue_lock);
- finish_wait(&rl->wait[rw], &wait);
+ finish_wait(&rl->wait[is_sync], &wait);

rq = get_request(q, rw_flags, bio, GFP_NOIO);
};
@@ -1070,14 +1070,14 @@ void __blk_put_request(struct request_queue *q, struct request *req)
* it didn't come out of our reserved rq pools
*/
if (req->cmd_flags & REQ_ALLOCED) {
- int rw = rq_data_dir(req);
+ int is_sync = rq_is_sync(req) != 0;
int priv = req->cmd_flags & REQ_ELVPRIV;

BUG_ON(!list_empty(&req->queuelist));
BUG_ON(!hlist_unhashed(&req->hash));

blk_free_request(q, req);
- freed_request(q, rw, priv);
+ freed_request(q, is_sync, priv);
}
}
EXPORT_SYMBOL_GPL(__blk_put_request);
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index e29ddfc..3ff9bba 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -48,28 +48,28 @@ queue_requests_store(struct request_queue *q, const char *page, size_t count)
q->nr_requests = nr;
blk_queue_congestion_threshold(q);

- if (rl->count[READ] >= queue_congestion_on_threshold(q))
- blk_set_queue_congested(q, READ);
- else if (rl->count[READ] < queue_congestion_off_threshold(q))
- blk_clear_queue_congested(q, READ);
-
- if (rl->count[WRITE] >= queue_congestion_on_threshold(q))
- blk_set_queue_congested(q, WRITE);
- else if (rl->count[WRITE] < queue_congestion_off_threshold(q))
- blk_clear_queue_congested(q, WRITE);
-
- if (rl->count[READ] >= q->nr_requests) {
- blk_set_queue_full(q, READ);
- } else if (rl->count[READ]+1 <= q->nr_requests) {
- blk_clear_queue_full(q, READ);
- wake_up(&rl->wait[READ]);
+ if (rl->count[BLK_RW_SYNC] >= queue_congestion_on_threshold(q))
+ blk_set_queue_congested(q, BLK_RW_SYNC);
+ else if (rl->count[BLK_RW_SYNC] < queue_congestion_off_threshold(q))
+ blk_clear_queue_congested(q, BLK_RW_SYNC);
+
+ if (rl->count[BLK_RW_ASYNC] >= queue_congestion_on_threshold(q))
+ blk_set_queue_congested(q, BLK_RW_ASYNC);
+ else if (rl->count[BLK_RW_ASYNC] < queue_congestion_off_threshold(q))
+ blk_clear_queue_congested(q, BLK_RW_ASYNC);
+
+ if (rl->count[BLK_RW_SYNC] >= q->nr_requests) {
+ blk_set_queue_full(q, BLK_RW_SYNC);
+ } else if (rl->count[BLK_RW_SYNC]+1 <= q->nr_requests) {
+ blk_clear_queue_full(q, BLK_RW_SYNC);
+ wake_up(&rl->wait[BLK_RW_SYNC]);
}

- if (rl->count[WRITE] >= q->nr_requests) {
- blk_set_queue_full(q, WRITE);
- } else if (rl->count[WRITE]+1 <= q->nr_requests) {
- blk_clear_queue_full(q, WRITE);
- wake_up(&rl->wait[WRITE]);
+ if (rl->count[BLK_RW_ASYNC] >= q->nr_requests) {
+ blk_set_queue_full(q, BLK_RW_ASYNC);
+ } else if (rl->count[BLK_RW_ASYNC]+1 <= q->nr_requests) {
+ blk_clear_queue_full(q, BLK_RW_ASYNC);
+ wake_up(&rl->wait[BLK_RW_ASYNC]);
}
spin_unlock_irq(q->queue_lock);
return ret;
diff --git a/block/elevator.c b/block/elevator.c
index 98259ed..ca6788a 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -677,7 +677,7 @@ void elv_insert(struct request_queue *q, struct request *rq, int where)
}

if (unplug_it && blk_queue_plugged(q)) {
- int nrq = q->rq.count[READ] + q->rq.count[WRITE]
+ int nrq = q->rq.count[BLK_RW_SYNC] + q->rq.count[BLK_RW_ASYNC]
- q->in_flight;

if (nrq >= q->unplug_thresh)
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index bee52ab..0ec2c59 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -24,8 +24,8 @@ struct dentry;
*/
enum bdi_state {
BDI_pdflush, /* A pdflush thread is working this device */
- BDI_write_congested, /* The write queue is getting full */
- BDI_read_congested, /* The read queue is getting full */
+ BDI_async_congested, /* The async (write) queue is getting full */
+ BDI_sync_congested, /* The sync queue is getting full */
BDI_unused, /* Available bits start here */
};

@@ -215,18 +215,18 @@ static inline int bdi_congested(struct backing_dev_info *bdi, int bdi_bits)

static inline int bdi_read_congested(struct backing_dev_info *bdi)
{
- return bdi_congested(bdi, 1 << BDI_read_congested);
+ return bdi_congested(bdi, 1 << BDI_sync_congested);
}

static inline int bdi_write_congested(struct backing_dev_info *bdi)
{
- return bdi_congested(bdi, 1 << BDI_write_congested);
+ return bdi_congested(bdi, 1 << BDI_async_congested);
}

static inline int bdi_rw_congested(struct backing_dev_info *bdi)
{
- return bdi_congested(bdi, (1 << BDI_read_congested)|
- (1 << BDI_write_congested));
+ return bdi_congested(bdi, (1 << BDI_sync_congested) |
+ (1 << BDI_async_congested));
}

void clear_bdi_congested(struct backing_dev_info *bdi, int rw);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 465d6ba..67dae3b 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -38,6 +38,10 @@ struct request;
typedef void (rq_end_io_fn)(struct request *, int);

struct request_list {
+ /*
+ * count[], starved[], and wait[] are indexed by
+ * BLK_RW_SYNC/BLK_RW_ASYNC
+ */
int count[2];
int starved[2];
int elvpriv;
@@ -66,6 +70,11 @@ enum rq_cmd_type_bits {
REQ_TYPE_ATA_PC,
};

+enum {
+ BLK_RW_ASYNC = 0,
+ BLK_RW_SYNC = 1,
+};
+
/*
* For request of type REQ_TYPE_LINUX_BLOCK, rq->cmd[0] is the opcode being
* sent down (similar to how REQ_TYPE_BLOCK_PC means that ->cmd[] holds a
@@ -103,7 +112,7 @@ enum rq_flag_bits {
__REQ_QUIET, /* don't worry about errors */
__REQ_PREEMPT, /* set for "ide_preempt" requests */
__REQ_ORDERED_COLOR, /* is before or after barrier */
- __REQ_RW_SYNC, /* request is sync (O_DIRECT) */
+ __REQ_RW_SYNC, /* request is sync (sync write or read) */
__REQ_ALLOCED, /* request came from our alloc pool */
__REQ_RW_META, /* metadata io request */
__REQ_COPY_USER, /* contains copies of user pages */
@@ -438,8 +447,8 @@ struct request_queue
#define QUEUE_FLAG_CLUSTER 0 /* cluster several segments into 1 */
#define QUEUE_FLAG_QUEUED 1 /* uses generic tag queueing */
#define QUEUE_FLAG_STOPPED 2 /* queue is stopped */
-#define QUEUE_FLAG_READFULL 3 /* read queue has been filled */
-#define QUEUE_FLAG_WRITEFULL 4 /* write queue has been filled */
+#define QUEUE_FLAG_SYNCFULL 3 /* read queue has been filled */
+#define QUEUE_FLAG_ASYNCFULL 4 /* write queue has been filled */
#define QUEUE_FLAG_DEAD 5 /* queue being torn down */
#define QUEUE_FLAG_REENTER 6 /* Re-entrancy avoidance */
#define QUEUE_FLAG_PLUGGED 7 /* queue is plugged */
@@ -611,32 +620,41 @@ enum {
#define rq_data_dir(rq) ((rq)->cmd_flags & 1)

/*
- * We regard a request as sync, if it's a READ or a SYNC write.
+ * We regard a request as sync, if either a read or a sync write
*/
-#define rq_is_sync(rq) (rq_data_dir((rq)) == READ || (rq)->cmd_flags & REQ_RW_SYNC)
+static inline bool rw_is_sync(unsigned int rw_flags)
+{
+ return !(rw_flags & REQ_RW) || (rw_flags & REQ_RW_SYNC);
+}
+
+static inline bool rq_is_sync(struct request *rq)
+{
+ return rw_is_sync(rq->cmd_flags);
+}
+
#define rq_is_meta(rq) ((rq)->cmd_flags & REQ_RW_META)

-static inline int blk_queue_full(struct request_queue *q, int rw)
+static inline int blk_queue_full(struct request_queue *q, int sync)
{
- if (rw == READ)
- return test_bit(QUEUE_FLAG_READFULL, &q->queue_flags);
- return test_bit(QUEUE_FLAG_WRITEFULL, &q->queue_flags);
+ if (sync)
+ return test_bit(QUEUE_FLAG_SYNCFULL, &q->queue_flags);
+ return test_bit(QUEUE_FLAG_ASYNCFULL, &q->queue_flags);
}

-static inline void blk_set_queue_full(struct request_queue *q, int rw)
+static inline void blk_set_queue_full(struct request_queue *q, int sync)
{
- if (rw == READ)
- queue_flag_set(QUEUE_FLAG_READFULL, q);
+ if (sync)
+ queue_flag_set(QUEUE_FLAG_SYNCFULL, q);
else
- queue_flag_set(QUEUE_FLAG_WRITEFULL, q);
+ queue_flag_set(QUEUE_FLAG_ASYNCFULL, q);
}

-static inline void blk_clear_queue_full(struct request_queue *q, int rw)
+static inline void blk_clear_queue_full(struct request_queue *q, int sync)
{
- if (rw == READ)
- queue_flag_clear(QUEUE_FLAG_READFULL, q);
+ if (sync)
+ queue_flag_clear(QUEUE_FLAG_SYNCFULL, q);
else
- queue_flag_clear(QUEUE_FLAG_WRITEFULL, q);
+ queue_flag_clear(QUEUE_FLAG_ASYNCFULL, q);
}


diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index be68c95..493b468 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -284,12 +284,12 @@ static wait_queue_head_t congestion_wqh[2] = {
};


-void clear_bdi_congested(struct backing_dev_info *bdi, int rw)
+void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
{
enum bdi_state bit;
- wait_queue_head_t *wqh = &congestion_wqh[rw];
+ wait_queue_head_t *wqh = &congestion_wqh[sync];

- bit = (rw == WRITE) ? BDI_write_congested : BDI_read_congested;
+ bit = sync ? BDI_sync_congested : BDI_async_congested;
clear_bit(bit, &bdi->state);
smp_mb__after_clear_bit();
if (waitqueue_active(wqh))
@@ -297,11 +297,11 @@ void clear_bdi_congested(struct backing_dev_info *bdi, int rw)
}
EXPORT_SYMBOL(clear_bdi_congested);

-void set_bdi_congested(struct backing_dev_info *bdi, int rw)
+void set_bdi_congested(struct backing_dev_info *bdi, int sync)
{
enum bdi_state bit;

- bit = (rw == WRITE) ? BDI_write_congested : BDI_read_congested;
+ bit = sync ? BDI_sync_congested : BDI_async_congested;
set_bit(bit, &bdi->state);
}
EXPORT_SYMBOL(set_bdi_congested);
--
1.6.2.1.423.g442d


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