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Date: Tue, 18 May 2021 12:26:03 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: "Matthew Wilcox (Oracle)" <willy@...radead.org>,
akpm@...ux-foundation.org
Cc: linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>,
Jeff Layton <jlayton@...nel.org>
Subject: Re: [PATCH v10 19/33] mm/filemap: Add folio_lock
On 5/11/21 11:47 PM, Matthew Wilcox (Oracle) wrote:
> This is like lock_page() but for use by callers who know they have a folio.
> Convert __lock_page() to be __folio_lock(). This saves one call to
> compound_head() per contended call to lock_page().
>
> Saves 362 bytes of text; mostly from improved register allocation and
> inlining decisions. __folio_lock is 59 bytes while __lock_page was 79.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> Reviewed-by: Christoph Hellwig <hch@....de>
> Acked-by: Jeff Layton <jlayton@...nel.org>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
> ---
> include/linux/pagemap.h | 24 +++++++++++++++++++-----
> mm/filemap.c | 29 +++++++++++++++--------------
> 2 files changed, 34 insertions(+), 19 deletions(-)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 8dbba0074536..9a78397609b8 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -638,7 +638,7 @@ static inline bool wake_page_match(struct wait_page_queue *wait_page,
> return true;
> }
>
> -extern void __lock_page(struct page *page);
> +void __folio_lock(struct folio *folio);
> 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,
> @@ -646,13 +646,24 @@ extern int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
> void unlock_page(struct page *page);
> void folio_unlock(struct folio *folio);
>
> +static inline bool folio_trylock(struct folio *folio)
> +{
> + return likely(!test_and_set_bit_lock(PG_locked, folio_flags(folio, 0)));
> +}
> +
> /*
> * Return true if the page was successfully locked
> */
> static inline int trylock_page(struct page *page)
> {
> - page = compound_head(page);
> - return (likely(!test_and_set_bit_lock(PG_locked, &page->flags)));
> + return folio_trylock(page_folio(page));
> +}
> +
> +static inline void folio_lock(struct folio *folio)
> +{
> + might_sleep();
> + if (!folio_trylock(folio))
> + __folio_lock(folio);
> }
>
> /*
> @@ -660,9 +671,12 @@ static inline int trylock_page(struct page *page)
> */
> static inline void lock_page(struct page *page)
> {
> + struct folio *folio;
> might_sleep();
> - if (!trylock_page(page))
> - __lock_page(page);
> +
> + folio = page_folio(page);
> + if (!folio_trylock(folio))
> + __folio_lock(folio);
> }
>
> /*
> diff --git a/mm/filemap.c b/mm/filemap.c
> index e7a6a58d6cd9..c6e5ba176764 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1187,7 +1187,7 @@ static void wake_up_page(struct page *page, int bit)
> */
> enum behavior {
> EXCLUSIVE, /* Hold ref to page and take the bit when woken, like
> - * __lock_page() waiting on then setting PG_locked.
> + * __folio_lock() waiting on then setting PG_locked.
> */
> SHARED, /* Hold ref to page and check the bit when woken, like
> * wait_on_page_writeback() waiting on PG_writeback.
> @@ -1576,17 +1576,16 @@ void page_endio(struct page *page, bool is_write, int err)
> EXPORT_SYMBOL_GPL(page_endio);
>
> /**
> - * __lock_page - get a lock on the page, assuming we need to sleep to get it
> - * @__page: the page to lock
> + * __folio_lock - Get a lock on the folio, assuming we need to sleep to get it.
> + * @folio: The folio to lock
> */
> -void __lock_page(struct page *__page)
> +void __folio_lock(struct folio *folio)
> {
> - struct page *page = compound_head(__page);
> - wait_queue_head_t *q = page_waitqueue(page);
> - wait_on_page_bit_common(q, page, PG_locked, TASK_UNINTERRUPTIBLE,
> + wait_queue_head_t *q = page_waitqueue(&folio->page);
> + wait_on_page_bit_common(q, &folio->page, PG_locked, TASK_UNINTERRUPTIBLE,
> EXCLUSIVE);
> }
> -EXPORT_SYMBOL(__lock_page);
> +EXPORT_SYMBOL(__folio_lock);
>
> int __lock_page_killable(struct page *__page)
> {
> @@ -1661,10 +1660,10 @@ int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
> return 0;
> }
> } else {
> - __lock_page(page);
> + __folio_lock(page_folio(page));
> }
> - return 1;
>
> + return 1;
> }
>
> /**
> @@ -2835,7 +2834,9 @@ loff_t mapping_seek_hole_data(struct address_space *mapping, loff_t start,
> static int lock_page_maybe_drop_mmap(struct vm_fault *vmf, struct page *page,
> struct file **fpin)
> {
> - if (trylock_page(page))
> + struct folio *folio = page_folio(page);
> +
> + if (folio_trylock(folio))
> return 1;
>
> /*
> @@ -2848,7 +2849,7 @@ static int lock_page_maybe_drop_mmap(struct vm_fault *vmf, struct page *page,
>
> *fpin = maybe_unlock_mmap_for_io(vmf, *fpin);
> if (vmf->flags & FAULT_FLAG_KILLABLE) {
> - if (__lock_page_killable(page)) {
> + if (__lock_page_killable(&folio->page)) {
> /*
> * We didn't have the right flags to drop the mmap_lock,
> * but all fault_handlers only check for fatal signals
> @@ -2860,11 +2861,11 @@ static int lock_page_maybe_drop_mmap(struct vm_fault *vmf, struct page *page,
> return 0;
> }
> } else
> - __lock_page(page);
> + __folio_lock(folio);
> +
> return 1;
> }
>
> -
> /*
> * Synchronous readahead happens when we don't even find a page in the page
> * cache at all. We don't want to perform IO under the mmap sem, so if we have
>
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