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io-wq: make buffered file write hashed work map per-ctx 

Before the io-wq thread change, we maintained a hash work map and lock
per-node per-ring. That wasn't ideal, as we really wanted it to be per
ring. But now that we have per-task workers, the hash map ends up being
just per-task. That'll work just fine for the normal case of having
one task use a ring, but if you share the ring between tasks, then it's
considerably worse than it was before.

Make the hash map per ctx instead, which provides full per-ctx buffered
write serialization on hashed writes.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2021-02-19 12:33:30 -07:00
parent eb2de9418d
commit e941894eae
3 changed files with 107 additions and 11 deletions
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85
fs/io-wq.c
View File

@ -87,7 +87,6 @@ struct io_wqe {
struct {
raw_spinlock_t lock;
struct io_wq_work_list work_list;
unsigned long hash_map;
unsigned flags;
} ____cacheline_aligned_in_smp;
@ -97,6 +96,8 @@ struct io_wqe {
struct hlist_nulls_head free_list;
struct list_head all_list;
struct wait_queue_entry wait;
struct io_wq *wq;
struct io_wq_work *hash_tail[IO_WQ_NR_HASH_BUCKETS];
};
@ -113,6 +114,9 @@ struct io_wq {
struct task_struct *manager;
struct user_struct *user;
struct io_wq_hash *hash;
refcount_t refs;
struct completion done;
@ -328,14 +332,31 @@ static inline unsigned int io_get_work_hash(struct io_wq_work *work)
return work->flags >> IO_WQ_HASH_SHIFT;
}
static void io_wait_on_hash(struct io_wqe *wqe, unsigned int hash)
{
struct io_wq *wq = wqe->wq;
spin_lock(&wq->hash->wait.lock);
if (list_empty(&wqe->wait.entry)) {
__add_wait_queue(&wq->hash->wait, &wqe->wait);
if (!test_bit(hash, &wq->hash->map)) {
__set_current_state(TASK_RUNNING);
list_del_init(&wqe->wait.entry);
}
}
spin_unlock(&wq->hash->wait.lock);
}
static struct io_wq_work *io_get_next_work(struct io_wqe *wqe)
__must_hold(wqe->lock)
{
struct io_wq_work_node *node, *prev;
struct io_wq_work *work, *tail;
unsigned int hash;
unsigned int stall_hash = -1U;
wq_list_for_each(node, prev, &wqe->work_list) {
unsigned int hash;
work = container_of(node, struct io_wq_work, list);
/* not hashed, can run anytime */
@ -344,16 +365,26 @@ static struct io_wq_work *io_get_next_work(struct io_wqe *wqe)
return work;
}
/* hashed, can run if not already running */
hash = io_get_work_hash(work);
if (!(wqe->hash_map & BIT(hash))) {
wqe->hash_map |= BIT(hash);
/* all items with this hash lie in [work, tail] */
tail = wqe->hash_tail[hash];
/* all items with this hash lie in [work, tail] */
tail = wqe->hash_tail[hash];
/* hashed, can run if not already running */
if (!test_and_set_bit(hash, &wqe->wq->hash->map)) {
wqe->hash_tail[hash] = NULL;
wq_list_cut(&wqe->work_list, &tail->list, prev);
return work;
}
if (stall_hash == -1U)
stall_hash = hash;
/* fast forward to a next hash, for-each will fix up @prev */
node = &tail->list;
}
if (stall_hash != -1U) {
raw_spin_unlock(&wqe->lock);
io_wait_on_hash(wqe, stall_hash);
raw_spin_lock(&wqe->lock);
}
return NULL;
@ -421,6 +452,7 @@ static void io_worker_handle_work(struct io_worker *worker)
if (!work)
break;
io_assign_current_work(worker, work);
__set_current_state(TASK_RUNNING);
/* handle a whole dependent link */
do {
@ -444,8 +476,10 @@ static void io_worker_handle_work(struct io_worker *worker)
io_wqe_enqueue(wqe, linked);
if (hash != -1U && !next_hashed) {
clear_bit(hash, &wq->hash->map);
if (wq_has_sleeper(&wq->hash->wait))
wake_up(&wq->hash->wait);
raw_spin_lock_irq(&wqe->lock);
wqe->hash_map &= ~BIT_ULL(hash);
wqe->flags &= ~IO_WQE_FLAG_STALLED;
/* skip unnecessary unlock-lock wqe->lock */
if (!work)
@ -471,7 +505,6 @@ static int io_wqe_worker(void *data)
loop:
raw_spin_lock_irq(&wqe->lock);
if (io_wqe_run_queue(wqe)) {
__set_current_state(TASK_RUNNING);
io_worker_handle_work(worker);
goto loop;
}
@ -928,6 +961,24 @@ enum io_wq_cancel io_wq_cancel_cb(struct io_wq *wq, work_cancel_fn *cancel,
return IO_WQ_CANCEL_NOTFOUND;
}
static int io_wqe_hash_wake(struct wait_queue_entry *wait, unsigned mode,
int sync, void *key)
{
struct io_wqe *wqe = container_of(wait, struct io_wqe, wait);
int ret;
list_del_init(&wait->entry);
rcu_read_lock();
ret = io_wqe_activate_free_worker(wqe);
rcu_read_unlock();
if (!ret)
wake_up_process(wqe->wq->manager);
return 1;
}
struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
{
int ret = -ENOMEM, node;
@ -948,6 +999,8 @@ struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
if (ret)
goto err_wqes;
refcount_inc(&data->hash->refs);
wq->hash = data->hash;
wq->free_work = data->free_work;
wq->do_work = data->do_work;
@ -968,6 +1021,8 @@ struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
wqe->acct[IO_WQ_ACCT_UNBOUND].max_workers =
task_rlimit(current, RLIMIT_NPROC);
atomic_set(&wqe->acct[IO_WQ_ACCT_UNBOUND].nr_running, 0);
wqe->wait.func = io_wqe_hash_wake;
INIT_LIST_HEAD(&wqe->wait.entry);
wqe->wq = wq;
raw_spin_lock_init(&wqe->lock);
INIT_WQ_LIST(&wqe->work_list);
@ -989,6 +1044,7 @@ struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
if (refcount_dec_and_test(&wq->refs))
complete(&wq->done);
io_wq_put_hash(data->hash);
err:
cpuhp_state_remove_instance_nocalls(io_wq_online, &wq->cpuhp_node);
for_each_node(node)
@ -1017,8 +1073,15 @@ void io_wq_destroy(struct io_wq *wq)
wait_for_completion(&wq->done);
for_each_node(node)
kfree(wq->wqes[node]);
spin_lock_irq(&wq->hash->wait.lock);
for_each_node(node) {
struct io_wqe *wqe = wq->wqes[node];
list_del_init(&wqe->wait.entry);
kfree(wqe);
}
spin_unlock_irq(&wq->hash->wait.lock);
io_wq_put_hash(wq->hash);
kfree(wq->wqes);
kfree(wq);
}

14
fs/io-wq.h
View File

@ -1,6 +1,7 @@
#ifndef INTERNAL_IO_WQ_H
#define INTERNAL_IO_WQ_H
#include <linux/refcount.h>
#include <linux/io_uring.h>
struct io_wq;
@ -93,7 +94,20 @@ static inline struct io_wq_work *wq_next_work(struct io_wq_work *work)
typedef struct io_wq_work *(free_work_fn)(struct io_wq_work *);
typedef void (io_wq_work_fn)(struct io_wq_work *);
struct io_wq_hash {
refcount_t refs;
unsigned long map;
struct wait_queue_head wait;
};
static inline void io_wq_put_hash(struct io_wq_hash *hash)
{
if (refcount_dec_and_test(&hash->refs))
kfree(hash);
}
struct io_wq_data {
struct io_wq_hash *hash;
io_wq_work_fn *do_work;
free_work_fn *free_work;
};

19
fs/io_uring.c
View File

@ -360,6 +360,9 @@ struct io_ring_ctx {
unsigned cached_cq_overflow;
unsigned long sq_check_overflow;
/* hashed buffered write serialization */
struct io_wq_hash *hash_map;
struct list_head defer_list;
struct list_head timeout_list;
struct list_head cq_overflow_list;
@ -454,6 +457,8 @@ struct io_ring_ctx {
/* exit task_work */
struct callback_head *exit_task_work;
struct wait_queue_head hash_wait;
/* Keep this last, we don't need it for the fast path */
struct work_struct exit_work;
};
@ -7763,9 +7768,21 @@ static struct io_wq_work *io_free_work(struct io_wq_work *work)
static struct io_wq *io_init_wq_offload(struct io_ring_ctx *ctx)
{
struct io_wq_hash *hash;
struct io_wq_data data;
unsigned int concurrency;
hash = ctx->hash_map;
if (!hash) {
hash = kzalloc(sizeof(*hash), GFP_KERNEL);
if (!hash)
return ERR_PTR(-ENOMEM);
refcount_set(&hash->refs, 1);
init_waitqueue_head(&hash->wait);
ctx->hash_map = hash;
}
data.hash = hash;
data.free_work = io_free_work;
data.do_work = io_wq_submit_work;
@ -8405,6 +8422,8 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
percpu_ref_exit(&ctx->refs);
free_uid(ctx->user);
io_req_caches_free(ctx, NULL);
if (ctx->hash_map)
io_wq_put_hash(ctx->hash_map);
kfree(ctx->cancel_hash);
kfree(ctx);
}