[PATCH v1 13/14] io_uring: support write throttling for async buffered writes

Stefan Roesch
2022-02-14T17:44:42Z

This adds the process-level throttling for the block layer for async
buffered writes to io-uring.In io_write the code now checks if the write
needs to be throttled. If this is required, it adds the request to the
list of pending io requests and starts a timer. After the timer expires,
it submits the list of pending writes.

- Add new list called pending_ios for delayed writes (throttled writes)
to struct io_uring_task. The list is protected by the task_lock spin
lock.
- Add new timer to struct io_uring_task.

Signed-off-by: Stefan Roesch <shr@fb.com>
---
fs/io_uring.c | 98 +++++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 91 insertions(+), 7 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 507f28b5b2bb..7bb77700ffac 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -461,6 +461,11 @@ struct io_ring_ctx {
};
};

+struct pending_list {
+ struct list_head list;
+ struct io_kiocb *req;
+};
+
struct io_uring_task {
/* submission side */
int cached_refs;
@@ -477,6 +482,9 @@ struct io_uring_task {
struct io_wq_work_list prior_task_list;
struct callback_head task_work;
bool task_running;
+
+ struct pending_list pending_ios;
+ struct timer_list timer;
};

/*
@@ -1134,13 +1142,14 @@ static void io_rsrc_put_work(struct work_struct *work);

static void io_req_task_queue(struct io_kiocb *req);
static void __io_submit_flush_completions(struct io_ring_ctx *ctx);
-static int io_req_prep_async(struct io_kiocb *req);
+static int io_req_prep_async(struct io_kiocb *req, bool force);

static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
unsigned int issue_flags, u32 slot_index);
static int io_close_fixed(struct io_kiocb *req, unsigned int issue_flags);

static enum hrtimer_restart io_link_timeout_fn(struct hrtimer *timer);
+static void delayed_write_fn(struct timer_list *tmr);

static struct kmem_cache *req_cachep;

@@ -2462,6 +2471,31 @@ static void io_req_task_queue_reissue(struct io_kiocb *req)
io_req_task_work_add(req, false);
}

+static int io_req_task_queue_reissue_delayed(struct io_kiocb *req)
+{
+ struct io_uring_task *tctx = req->task->io_uring;
+ struct pending_list *pending = kmalloc(sizeof(struct pending_list), GFP_KERNEL);
+ bool empty;
+
+ if (!pending)
+ return -ENOMEM;
+ pending->req = req;
+
+ spin_lock_irq(&tctx->task_lock);
+ empty = list_empty(&tctx->pending_ios.list);
+ list_add_tail(&pending->list, &tctx->pending_ios.list);
+
+ if (empty) {
+ timer_setup(&tctx->timer, delayed_write_fn, 0);
+
+ tctx->timer.expires = current->bdp_pause;
+ add_timer(&tctx->timer);
+ }
+ spin_unlock_irq(&tctx->task_lock);
+
+ return 0;
+}
+
static inline void io_queue_next(struct io_kiocb *req)
{
struct io_kiocb *nxt = io_req_find_next(req);
@@ -2770,7 +2804,7 @@ static bool io_resubmit_prep(struct io_kiocb *req)
struct io_async_rw *rw = req->async_data;

if (!req_has_async_data(req))
- return !io_req_prep_async(req);
+ return !io_req_prep_async(req, false);
iov_iter_restore(&rw->s.iter, &rw->s.iter_state);
return true;
}
@@ -3751,6 +3785,38 @@ static int io_write_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
return io_prep_rw(req, sqe);
}

+static inline unsigned long write_delay(void)
+{
+ if (likely(current->bdp_nr_dirtied_pause == -1 ||
+ !time_before(jiffies, current->bdp_pause)))
+ return 0;
+
+ return current->bdp_pause;
+}
+
+static void delayed_write_fn(struct timer_list *tmr)
+{
+ struct io_uring_task *tctx = from_timer(tctx, tmr, timer);
+ struct list_head *curr;
+ struct list_head *next;
+ LIST_HEAD(pending_ios);
+
+ /* Move list to temporary list. */
+ spin_lock_irq(&tctx->task_lock);
+ list_splice_init(&tctx->pending_ios.list, &pending_ios);
+ spin_unlock_irq(&tctx->task_lock);
+
+ list_for_each_safe(curr, next, &pending_ios) {
+ struct pending_list *io;
+
+ io = list_entry(curr, struct pending_list, list);
+ io_req_task_queue_reissue(io->req);
+
+ list_del(curr);
+ kfree(io);
+ }
+}
+
static int io_write(struct io_kiocb *req, unsigned int issue_flags)
{
struct io_rw_state __s, *s = &__s;
@@ -3759,6 +3825,18 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
ssize_t ret, ret2;

+ /* Write throttling active? */
+ if (unlikely(write_delay()) && !(kiocb->ki_flags & IOCB_DIRECT)) {
+ int ret = io_req_prep_async(req, true);
+
+ if (unlikely(ret))
+ io_req_complete_failed(req, ret);
+ else
+ ret = io_req_task_queue_reissue_delayed(req);
+
+ return ret;
+ }
+
if (!req_has_async_data(req)) {
ret = io_import_iovec(WRITE, req, &iovec, s, issue_flags);
if (unlikely(ret < 0))
@@ -6597,9 +6675,9 @@ static int io_req_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
return -EINVAL;
}

-static int io_req_prep_async(struct io_kiocb *req)
+static int io_req_prep_async(struct io_kiocb *req, bool force)
{
- if (!io_op_defs[req->opcode].needs_async_setup)
+ if (!force && !io_op_defs[req->opcode].needs_async_setup)
return 0;
if (WARN_ON_ONCE(req_has_async_data(req)))
return -EFAULT;
@@ -6609,6 +6687,10 @@ static int io_req_prep_async(struct io_kiocb *req)
switch (req->opcode) {
case IORING_OP_READV:
return io_rw_prep_async(req, READ);
+ case IORING_OP_WRITE:
+ if (!force)
+ break;
+ fallthrough;
case IORING_OP_WRITEV:
return io_rw_prep_async(req, WRITE);
case IORING_OP_SENDMSG:
@@ -6618,6 +6700,7 @@ static int io_req_prep_async(struct io_kiocb *req)
case IORING_OP_CONNECT:
return io_connect_prep_async(req);
}
+
printk_once(KERN_WARNING "io_uring: prep_async() bad opcode %d\n",
req->opcode);
return -EFAULT;
@@ -6651,7 +6734,7 @@ static __cold void io_drain_req(struct io_kiocb *req)
}
spin_unlock(&ctx->completion_lock);

- ret = io_req_prep_async(req);
+ ret = io_req_prep_async(req, false);
if (ret) {
fail:
io_req_complete_failed(req, ret);
@@ -7146,7 +7229,7 @@ static void io_queue_sqe_fallback(struct io_kiocb *req)
} else if (unlikely(req->ctx->drain_active)) {
io_drain_req(req);
} else {
- int ret = io_req_prep_async(req);
+ int ret = io_req_prep_async(req, false);

if (unlikely(ret))
io_req_complete_failed(req, ret);
@@ -7345,7 +7428,7 @@ static int io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
struct io_kiocb *head = link->head;

if (!(req->flags & REQ_F_FAIL)) {
- ret = io_req_prep_async(req);
+ ret = io_req_prep_async(req, false);
if (unlikely(ret)) {
req_fail_link_node(req, ret);
if (!(head->flags & REQ_F_FAIL))
@@ -8785,6 +8868,7 @@ static __cold int io_uring_alloc_task_context(struct task_struct *task,
INIT_WQ_LIST(&tctx->task_list);
INIT_WQ_LIST(&tctx->prior_task_list);
init_task_work(&tctx->task_work, tctx_task_work);
+ INIT_LIST_HEAD(&tctx->pending_ios.list);
return 0;
}

--
2.30.2