Commit bb43b14b authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

mm: delete __ClearPageWaiters() 

The PG_waiters bit is not included in PAGE_FLAGS_CHECK_AT_FREE, and
vmscan.c's free_unref_page_list() callers rely on that not to generate
bad_page() alerts.  So __page_cache_release(), put_pages_list() and
release_pages() (and presumably copy-and-pasted free_zone_device_page())
are redundant and misleading to make a special point of clearing it (as
the "__" implies, it could only safely be used on the freeing path).

Delete __ClearPageWaiters().  Remark on this in one of the "possible"
comments in folio_wake_bit(), and delete the superfluous comments.

Link: https://lkml.kernel.org/r/3eafa969-5b1a-accf-88fe-318784c791a@google.com


Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Tested-by: default avatarYu Zhao <yuzhao@google.com>
Reviewed-by: default avatarYang Shi <shy828301@gmail.com>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6f6a841f

include/linux/page-flags.h

+1 −1
Original line number Diff line number Diff line
@@ -481,7 +481,7 @@ static inline int TestClearPage##uname(struct page *page) { return 0; } 
	TESTSETFLAG_FALSE(uname, lname) TESTCLEARFLAG_FALSE(uname, lname)



__PAGEFLAG(Locked, locked, PF_NO_TAIL)

PAGEFLAG(Waiters, waiters, PF_ONLY_HEAD) __CLEARPAGEFLAG(Waiters, waiters, PF_ONLY_HEAD)

PAGEFLAG(Waiters, waiters, PF_ONLY_HEAD)

PAGEFLAG(Error, error, PF_NO_TAIL) TESTCLEARFLAG(Error, error, PF_NO_TAIL)

PAGEFLAG(Referenced, referenced, PF_HEAD)

	TESTCLEARFLAG(Referenced, referenced, PF_HEAD)

mm/filemap.c

+8 −15
Original line number Diff line number Diff line
@@ -1185,24 +1185,17 @@ static void folio_wake_bit(struct folio *folio, int bit_nr) 
	}



	/*

	 * It is possible for other pages to have collided on the waitqueue

	 * hash, so in that case check for a page match. That prevents a long-

	 * term waiter

	 * It's possible to miss clearing waiters here, when we woke our page

	 * waiters, but the hashed waitqueue has waiters for other pages on it.

	 * That's okay, it's a rare case. The next waker will clear it.

	 *

	 * It is still possible to miss a case here, when we woke page waiters

	 * and removed them from the waitqueue, but there are still other

	 * page waiters.

	 * Note that, depending on the page pool (buddy, hugetlb, ZONE_DEVICE,

	 * other), the flag may be cleared in the course of freeing the page;

	 * but that is not required for correctness.

	 */

	if (!waitqueue_active(q) || !key.page_match) {

	if (!waitqueue_active(q) || !key.page_match)

		folio_clear_waiters(folio);

		/*

		 * It's possible to miss clearing Waiters here, when we woke

		 * our page waiters, but the hashed waitqueue has waiters for

		 * other pages on it.

		 *

		 * That's okay, it's a rare case. The next waker will clear it.

		 */

	}



	spin_unlock_irqrestore(&q->lock, flags);

}

mm/memremap.c

+0 −2
Original line number Diff line number Diff line
@@ -456,8 +456,6 @@ void free_zone_device_page(struct page *page) 
	if (WARN_ON_ONCE(!page->pgmap->ops || !page->pgmap->ops->page_free))

		return;



	__ClearPageWaiters(page);



	mem_cgroup_uncharge(page_folio(page));



	/*

mm/swap.c

+0 −4
Original line number Diff line number Diff line
@@ -97,7 +97,6 @@ static void __page_cache_release(struct page *page) 
		mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);

		count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages);

	}

	__ClearPageWaiters(page);

}



static void __put_single_page(struct page *page)
@@ -152,7 +151,6 @@ void put_pages_list(struct list_head *pages) 
			continue;

		}

		/* Cannot be PageLRU because it's passed to us using the lru */

		__ClearPageWaiters(page);

	}



	free_unref_page_list(pages);
@@ -971,8 +969,6 @@ void release_pages(struct page **pages, int nr) 
			count_vm_event(UNEVICTABLE_PGCLEARED);

		}



		__ClearPageWaiters(page);



		list_add(&page->lru, &pages_to_free);

	}

	if (lruvec)