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aio: use cancellation list lazily

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Cancelling kiocbs requires adding them to a per kioctx linked list,
which is one of the few things we need to take the kioctx lock for in
the fast path.  But most kiocbs can't be cancelled - so if we just do
this lazily, we can avoid quite a bit of locking overhead.

While we're at it, instead of using a flag bit switch to using ki_cancel
itself to indicate that a kiocb has been cancelled/completed.  This lets
us get rid of ki_flags entirely.

[[email protected]: remove buggy BUG()]
Signed-off-by: Kent Overstreet <[email protected]>
Cc: Zach Brown <[email protected]>
Cc: Felipe Balbi <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Mark Fasheh <[email protected]>
Cc: Joel Becker <[email protected]>
Cc: Rusty Russell <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Asai Thambi S P <[email protected]>
Cc: Selvan Mani <[email protected]>
Cc: Sam Bradshaw <[email protected]>
Cc: Jeff Moyer <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Benjamin LaHaise <[email protected]>
Reviewed-by: "Theodore Ts'o" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Kent Overstreet 2013-05-07 16:18:49 -07:00 • committed by Linus Torvalds
commit 0460fef2a9
3 changed files with 81 additions and 55 deletions
Download patch file Download diff file Expand all files Collapse all files

106
fs/aio.c
View file

@ -97,6 +97,8 @@ struct kioctx {
struct aio_ring_info ring_info;
spinlock_t completion_lock;
struct rcu_head rcu_head;
struct work_struct rcu_work;
};
@ -220,25 +222,51 @@ static int aio_setup_ring(struct kioctx *ctx)
#define AIO_EVENTS_FIRST_PAGE ((PAGE_SIZE - sizeof(struct aio_ring)) / sizeof(struct io_event))
#define AIO_EVENTS_OFFSET (AIO_EVENTS_PER_PAGE - AIO_EVENTS_FIRST_PAGE)
void kiocb_set_cancel_fn(struct kiocb *req, kiocb_cancel_fn *cancel)
{
struct kioctx *ctx = req->ki_ctx;
unsigned long flags;
spin_lock_irqsave(&ctx->ctx_lock, flags);
if (!req->ki_list.next)
list_add(&req->ki_list, &ctx->active_reqs);
req->ki_cancel = cancel;
spin_unlock_irqrestore(&ctx->ctx_lock, flags);
}
EXPORT_SYMBOL(kiocb_set_cancel_fn);
static int kiocb_cancel(struct kioctx *ctx, struct kiocb *kiocb,
struct io_event *res)
{
int (*cancel)(struct kiocb *, struct io_event *);
kiocb_cancel_fn *old, *cancel;
int ret = -EINVAL;
cancel = kiocb->ki_cancel;
kiocbSetCancelled(kiocb);
if (cancel) {
atomic_inc(&kiocb->ki_users);
spin_unlock_irq(&ctx->ctx_lock);
/*
* Don't want to set kiocb->ki_cancel = KIOCB_CANCELLED unless it
* actually has a cancel function, hence the cmpxchg()
*/
memset(res, 0, sizeof(*res));
res->obj = (u64)(unsigned long)kiocb->ki_obj.user;
res->data = kiocb->ki_user_data;
ret = cancel(kiocb, res);
cancel = ACCESS_ONCE(kiocb->ki_cancel);
do {
if (!cancel || cancel == KIOCB_CANCELLED)
return ret;
spin_lock_irq(&ctx->ctx_lock);
}
old = cancel;
cancel = cmpxchg(&kiocb->ki_cancel, old, KIOCB_CANCELLED);
} while (cancel != old);
atomic_inc(&kiocb->ki_users);
spin_unlock_irq(&ctx->ctx_lock);
memset(res, 0, sizeof(*res));
res->obj = (u64)(unsigned long)kiocb->ki_obj.user;
res->data = kiocb->ki_user_data;
ret = cancel(kiocb, res);
spin_lock_irq(&ctx->ctx_lock);
return ret;
}
@ -326,6 +354,7 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
atomic_set(&ctx->users, 2);
atomic_set(&ctx->dead, 0);
spin_lock_init(&ctx->ctx_lock);
spin_lock_init(&ctx->completion_lock);
mutex_init(&ctx->ring_info.ring_lock);
init_waitqueue_head(&ctx->wait);
@ -468,20 +497,12 @@ static struct kiocb *__aio_get_req(struct kioctx *ctx)
{
struct kiocb *req = NULL;
req = kmem_cache_alloc(kiocb_cachep, GFP_KERNEL);
req = kmem_cache_alloc(kiocb_cachep, GFP_KERNEL|__GFP_ZERO);
if (unlikely(!req))
return NULL;
req->ki_flags = 0;
atomic_set(&req->ki_users, 2);
req->ki_key = 0;
req->ki_ctx = ctx;
req->ki_cancel = NULL;
req->ki_retry = NULL;
req->ki_dtor = NULL;
req->private = NULL;
req->ki_iovec = NULL;
req->ki_eventfd = NULL;
return req;
}
@ -512,7 +533,6 @@ static void kiocb_batch_free(struct kioctx *ctx, struct kiocb_batch *batch)
spin_lock_irq(&ctx->ctx_lock);
list_for_each_entry_safe(req, n, &batch->head, ki_batch) {
list_del(&req->ki_batch);
list_del(&req->ki_list);
kmem_cache_free(kiocb_cachep, req);
atomic_dec(&ctx->reqs_active);
}
@ -559,10 +579,7 @@ static int kiocb_batch_refill(struct kioctx *ctx, struct kiocb_batch *batch)
}
batch->count -= allocated;
list_for_each_entry(req, &batch->head, ki_batch) {
list_add(&req->ki_list, &ctx->active_reqs);
atomic_inc(&ctx->reqs_active);
}
atomic_add(allocated, &ctx->reqs_active);
kunmap_atomic(ring);
spin_unlock_irq(&ctx->ctx_lock);
@ -653,25 +670,34 @@ void aio_complete(struct kiocb *iocb, long res, long res2)
info = &ctx->ring_info;
/*
* Add a completion event to the ring buffer. Must be done holding
* ctx->ctx_lock to prevent other code from messing with the tail
* pointer since we might be called from irq context.
*
* Take rcu_read_lock() in case the kioctx is being destroyed, as we
* need to issue a wakeup after decrementing reqs_active.
*/
rcu_read_lock();
spin_lock_irqsave(&ctx->ctx_lock, flags);
list_del(&iocb->ki_list); /* remove from active_reqs */
if (iocb->ki_list.next) {
unsigned long flags;
spin_lock_irqsave(&ctx->ctx_lock, flags);
list_del(&iocb->ki_list);
spin_unlock_irqrestore(&ctx->ctx_lock, flags);
}
/*
* cancelled requests don't get events, userland was given one
* when the event got cancelled.
*/
if (kiocbIsCancelled(iocb))
if (unlikely(xchg(&iocb->ki_cancel,
KIOCB_CANCELLED) == KIOCB_CANCELLED))
goto put_rq;
/*
* Add a completion event to the ring buffer. Must be done holding
* ctx->ctx_lock to prevent other code from messing with the tail
* pointer since we might be called from irq context.
*/
spin_lock_irqsave(&ctx->completion_lock, flags);
tail = info->tail;
pos = tail + AIO_EVENTS_OFFSET;
@ -705,6 +731,8 @@ void aio_complete(struct kiocb *iocb, long res, long res2)
kunmap_atomic(ring);
flush_dcache_page(info->ring_pages[0]);
spin_unlock_irqrestore(&ctx->completion_lock, flags);
pr_debug("added to ring %p at [%u]\n", iocb, tail);
/*
@ -731,7 +759,6 @@ put_rq:
if (waitqueue_active(&ctx->wait))
wake_up(&ctx->wait);
spin_unlock_irqrestore(&ctx->ctx_lock, flags);
rcu_read_unlock();
}
EXPORT_SYMBOL(aio_complete);
@ -1216,15 +1243,10 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
req->ki_opcode = iocb->aio_lio_opcode;
ret = aio_setup_iocb(req, compat);
if (ret)
goto out_put_req;
if (unlikely(kiocbIsCancelled(req)))
ret = -EINTR;
else
ret = req->ki_retry(req);
ret = req->ki_retry(req);
if (ret != -EIOCBQUEUED) {
/*
* There's no easy way to restart the syscall since other AIO's
@ -1241,10 +1263,6 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
return 0;
out_put_req:
spin_lock_irq(&ctx->ctx_lock);
list_del(&req->ki_list);
spin_unlock_irq(&ctx->ctx_lock);
atomic_dec(&ctx->reqs_active);
aio_put_req(req); /* drop extra ref to req */
aio_put_req(req); /* drop i/o ref to req */