The patch titled
Subject: mm: delete __ClearPageWaiters()
has been added to the -mm tree. Its filename is
mm-delete-__clearpagewaiters.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-delete-__clearpagewaiters.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-delete-__clearpagewaiters.patch
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------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: 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@xxxxxxxxxx
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Tested-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/page-flags.h | 2 +-
mm/filemap.c | 23 ++++++++---------------
mm/memremap.c | 2 --
mm/swap.c | 4 ----
4 files changed, 9 insertions(+), 22 deletions(-)
--- a/include/linux/page-flags.h~mm-delete-__clearpagewaiters
+++ a/include/linux/page-flags.h
@@ -412,7 +412,7 @@ static inline int TestClearPage##uname(s
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)
--- a/mm/filemap.c~mm-delete-__clearpagewaiters
+++ a/mm/filemap.c
@@ -1174,24 +1174,17 @@ static void folio_wake_bit(struct folio
}
/*
- * 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);
}
--- a/mm/memremap.c~mm-delete-__clearpagewaiters
+++ a/mm/memremap.c
@@ -495,8 +495,6 @@ void free_devmap_managed_page(struct pag
return;
}
- __ClearPageWaiters(page);
-
mem_cgroup_uncharge(page_folio(page));
/*
--- a/mm/swap.c~mm-delete-__clearpagewaiters
+++ a/mm/swap.c
@@ -89,7 +89,6 @@ static void __page_cache_release(struct
__clear_page_lru_flags(page);
unlock_page_lruvec_irqrestore(lruvec, flags);
}
- __ClearPageWaiters(page);
}
static void __put_single_page(struct page *page)
@@ -152,7 +151,6 @@ void put_pages_list(struct list_head *pa
continue;
}
/* Cannot be PageLRU because it's passed to us using the lru */
- __ClearPageWaiters(page);
}
free_unref_page_list(pages);
@@ -969,8 +967,6 @@ void release_pages(struct page **pages,
__clear_page_lru_flags(page);
}
- __ClearPageWaiters(page);
-
list_add(&page->lru, &pages_to_free);
}
if (lruvec)
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
mm-delete-__clearpagewaiters.patch
tmpfs-support-for-file-creation-time-fix.patch
mm-_install_special_mapping-apply-vm_locked_clear_mask.patch
mm-thp-refix-__split_huge_pmd_locked-for-migration-pmd.patch
mm-thp-clearpagedoublemap-in-first-page_add_file_rmap.patch
mm-thp-fix-nr_file_mapped-accounting-in-page__file_rmap.patch
