| Message ID | 20200618144355.17324-8-axboe@kernel.dk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [01/15] block: provide plug based way of signaling forced no-wait semantics | expand |
Jens, Am Do., 18. Juni 2020 um 16:47 Uhr schrieb Jens Axboe <axboe@kernel.dk>: > 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> > --- > 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; > + } This hunk should have been part of "mm: allow read-ahead with IOCB_NOWAIT set" ... > /* > * 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 > Andreas
On 7/7/20 5:32 AM, Andreas Grünbacher wrote: >> @@ -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; >> + } > > This hunk should have been part of "mm: allow read-ahead with > IOCB_NOWAIT set" ... It probably should have... Oh well, it's been queued up multiple weeks at this point, not worth rebasing to move this hunk.
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)) {