Commit dd3e6d50 authored by Jens Axboe's avatar Jens Axboe

mm: add support for async page locking

Normally waiting for a page to become unlocked, or locking the page,
requires waiting for IO to complete. Add support for lock_page_async()
and wait_on_page_locked_async(), which are callback based instead. This
allows a caller to get notified when a page becomes unlocked, rather
than wait for it.

We add a new iocb field, ki_waitq, to pass in the necessary data for this
to happen. We can unionize this with ki_cookie, since that is only used
for polled IO. Polled IO can never co-exist with async callbacks, as it is
(by definition) polled completions. struct wait_page_key is made public,
and we define struct wait_page_async as the interface between the caller
and the core.
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent c7510ab2
......@@ -315,6 +315,8 @@ enum rw_hint {
#define IOCB_SYNC (1 << 5)
#define IOCB_WRITE (1 << 6)
#define IOCB_NOWAIT (1 << 7)
/* iocb->ki_waitq is valid */
#define IOCB_WAITQ (1 << 8)
struct kiocb {
struct file *ki_filp;
......@@ -328,7 +330,10 @@ struct kiocb {
int ki_flags;
u16 ki_hint;
u16 ki_ioprio; /* See linux/ioprio.h */
union {
unsigned int ki_cookie; /* for ->iopoll */
struct wait_page_queue *ki_waitq; /* for async buffered IO */
};
randomized_struct_fields_end
};
......
......@@ -535,6 +535,7 @@ static inline int wake_page_match(struct wait_page_queue *wait_page,
extern void __lock_page(struct page *page);
extern int __lock_page_killable(struct page *page);
extern int __lock_page_async(struct page *page, struct wait_page_queue *wait);
extern int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
unsigned int flags);
extern void unlock_page(struct page *page);
......@@ -571,6 +572,22 @@ static inline int lock_page_killable(struct page *page)
return 0;
}
/*
* lock_page_async - Lock the page, unless this would block. If the page
* is already locked, then queue a callback when the page becomes unlocked.
* This callback can then retry the operation.
*
* Returns 0 if the page is locked successfully, or -EIOCBQUEUED if the page
* was already locked and the callback defined in 'wait' was queued.
*/
static inline int lock_page_async(struct page *page,
struct wait_page_queue *wait)
{
if (!trylock_page(page))
return __lock_page_async(page, wait);
return 0;
}
/*
* lock_page_or_retry - Lock the page, unless this would block and the
* caller indicated that it can handle a retry.
......
......@@ -1180,6 +1180,36 @@ int wait_on_page_bit_killable(struct page *page, int bit_nr)
}
EXPORT_SYMBOL(wait_on_page_bit_killable);
static int __wait_on_page_locked_async(struct page *page,
struct wait_page_queue *wait, bool set)
{
struct wait_queue_head *q = page_waitqueue(page);
int ret = 0;
wait->page = page;
wait->bit_nr = PG_locked;
spin_lock_irq(&q->lock);
__add_wait_queue_entry_tail(q, &wait->wait);
SetPageWaiters(page);
if (set)
ret = !trylock_page(page);
else
ret = PageLocked(page);
/*
* If we were succesful now, we know we're still on the
* waitqueue as we're still under the lock. This means it's
* safe to remove and return success, we know the callback
* isn't going to trigger.
*/
if (!ret)
__remove_wait_queue(q, &wait->wait);
else
ret = -EIOCBQUEUED;
spin_unlock_irq(&q->lock);
return ret;
}
/**
* put_and_wait_on_page_locked - Drop a reference and wait for it to be unlocked
* @page: The page to wait for.
......@@ -1342,6 +1372,11 @@ int __lock_page_killable(struct page *__page)
}
EXPORT_SYMBOL_GPL(__lock_page_killable);
int __lock_page_async(struct page *page, struct wait_page_queue *wait)
{
return __wait_on_page_locked_async(page, wait, true);
}
/*
* Return values:
* 1 - page is locked; mmap_lock is still held.
......@@ -2131,6 +2166,11 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
}
readpage:
if (iocb->ki_flags & IOCB_NOWAIT) {
unlock_page(page);
put_page(page);
goto would_block;
}
/*
* A previous I/O error may have been due to temporary
* failures, eg. multipath errors.
......@@ -2150,6 +2190,9 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
}
if (!PageUptodate(page)) {
if (iocb->ki_flags & IOCB_WAITQ)
error = lock_page_async(page, iocb->ki_waitq);
else
error = lock_page_killable(page);
if (unlikely(error))
goto readpage_error;
......
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