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: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
include/linux/fs.h | 7 ++++++-
include/linux/pagemap.h | 17 ++++++++++++++++
mm/filemap.c | 45 ++++++++++++++++++++++++++++++++++++++++-
3 files changed, 67 insertions(+), 2 deletions(-)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6c4ab4dc1cd7..6ac919b40596 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -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 */
- unsigned int ki_cookie; /* for ->iopoll */
+ union {
+ unsigned int ki_cookie; /* for ->iopoll */
+ struct wait_page_queue *ki_waitq; /* for async buffered IO */
+ };
randomized_struct_fields_end
};
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 2f18221bb5c8..e053e1d9a4d7 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -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.
diff --git a/mm/filemap.c b/mm/filemap.c
index c3175dbd8fba..e8aaf43bee9f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -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.
@@ -2150,7 +2190,10 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
}
if (!PageUptodate(page)) {
- error = lock_page_killable(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;
if (!PageUptodate(page)) {
--
2.27.0
