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>

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 88fe1d7..9d8eeaa 100644 (file)
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -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)

diff --git a/mm/filemap.c b/mm/filemap.c
index d2e6a79..98dfeff 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -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);
 }
 

diff --git a/mm/memremap.c b/mm/memremap.c
index c17eca4..af02236 100644 (file)
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -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));
 
        /*

diff --git a/mm/swap.c b/mm/swap.c
index 5b30045..bceff0c 100644 (file)
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -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)