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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: Hugh Dickins <hughd@google.com>
Tested-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Reviewed-by: David 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2022-03-24 18:09:49 -07:00 committed by Linus Torvalds
parent 6f6a841fb7
commit bb43b14b57
4 changed files with 9 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/page-flags.h
View File

@ -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)

23
mm/filemap.c
View File

@ -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);
}

2
mm/memremap.c
View File

@ -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));
/*

4
mm/swap.c
View File

@ -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)