From: Hugh Dickins <hughd@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>,
Nicholas Piggin <npiggin@gmail.com>, Yu Zhao <yuzhao@google.com>,
Yang Shi <shy828301@gmail.com>, Michal Hocko <mhocko@suse.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: [PATCH mmotm] mm: delete __ClearPageWaiters()
Date: Wed, 2 Mar 2022 17:56:11 -0800 (PST) [thread overview]
Message-ID: <351df0af-78f2-c20-2a6d-e5f978e5ca1@google.com> (raw)
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() and release_pages() (and
the presumably copy-and-pasted put_zone_device_private_or_public_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 wake_up_page_bit(), and delete the superfluous comments.
Signed-off-by: Hugh Dickins <hughd@google.com>
---
We've used this since 2018, and I see Yu Zhao posted similar in 2020:
https://lore.kernel.org/linux-mm/20200818184704.3625199-3-yuzhao@google.com/
I couldn't join in at that time, but think its reception was over-cautious.
include/linux/page-flags.h | 2 +-
mm/filemap.c | 22 +++++++---------------
mm/memremap.c | 2 --
mm/swap.c | 4 ----
4 files changed, 8 insertions(+), 22 deletions(-)
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -481,7 +481,7 @@ static unsigned long *folio_flags(struct folio *folio, unsigned n)
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
+++ b/mm/filemap.c
@@ -1179,24 +1179,16 @@ 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.
*
- * 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.
+ * That's okay, it's a rare case. The next waker will clear it. Or,
+ * it might be left set until the page is freed: when it's masked off
+ * with others in PAGE_FLAGS_CHECK_AT_PREP, by free_pages_prepare().
*/
- 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
+++ b/mm/memremap.c
@@ -487,8 +487,6 @@ 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));
/*
--- 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);
@@ -966,8 +964,6 @@ void release_pages(struct page **pages, int nr)
count_vm_event(UNEVICTABLE_PGCLEARED);
}
- __ClearPageWaiters(page);
-
list_add(&page->lru, &pages_to_free);
}
if (lruvec)
next reply other threads:[~2022-03-03 1:56 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-03 1:56 Hugh Dickins [this message]
2022-03-03 2:15 ` [PATCH mmotm] mm: delete __ClearPageWaiters() Yu Zhao
2022-03-03 8:54 ` David Hildenbrand
2022-03-03 22:28 ` Hugh Dickins
2022-03-03 22:41 ` Matthew Wilcox
2022-03-04 17:25 ` David Hildenbrand
2022-03-04 21:17 ` Hugh Dickins
2022-03-04 21:25 ` [PATCH mmotm v2] " Hugh Dickins
2022-03-07 8:41 ` David Hildenbrand
2022-03-07 20:17 ` Yang Shi
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