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mm: add support for async page locking

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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@cmpxchg.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2020-05-22 09:12:09 -06:00
parent c7510ab2cf
commit dd3e6d5039
3 changed files with 67 additions and 2 deletions
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7
include/linux/fs.h
View file

@ -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
};

17
include/linux/pagemap.h
View file

@ -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.