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From:   "Matthew Wilcox (Oracle)" <willy@infradead.org>
To:     Bin Lai <sclaibin@gmail.com>
Cc:     "Matthew Wilcox (Oracle)" <willy@infradead.org>, mingo@redhat.com,
        peterz@infradead.org, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, akpm@linux-foundation.org,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org
Subject: [PATCH 1/2] filemap: Remove use of wait bookmarks
Date:   Tue, 10 Oct 2023 04:58:28 +0100
Message-Id: <20231010035829.544242-1-willy@infradead.org>
In-Reply-To: <20231010032833.398033-1-robinlai@tencent.com>
References: <20231010032833.398033-1-robinlai@tencent.com>
MIME-Version: 1.0
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The original problem of the overly long list of waiters on a
locked page was solved properly by commit 9a1ea439b16b ("mm:
put_and_wait_on_page_locked() while page is migrated").  In
the meantime, using bookmarks for the writeback bit can cause
livelocks, so we need to stop using them.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/filemap.c | 21 +--------------------
 1 file changed, 1 insertion(+), 20 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index f0a15ce1bd1b..1f9adad2d781 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1135,32 +1135,13 @@ static void folio_wake_bit(struct folio *folio, int bit_nr)
 	wait_queue_head_t *q = folio_waitqueue(folio);
 	struct wait_page_key key;
 	unsigned long flags;
-	wait_queue_entry_t bookmark;
 
 	key.folio = folio;
 	key.bit_nr = bit_nr;
 	key.page_match = 0;
 
-	bookmark.flags = 0;
-	bookmark.private = NULL;
-	bookmark.func = NULL;
-	INIT_LIST_HEAD(&bookmark.entry);
-
 	spin_lock_irqsave(&q->lock, flags);
-	__wake_up_locked_key_bookmark(q, TASK_NORMAL, &key, &bookmark);
-
-	while (bookmark.flags & WQ_FLAG_BOOKMARK) {
-		/*
-		 * Take a breather from holding the lock,
-		 * allow pages that finish wake up asynchronously
-		 * to acquire the lock and remove themselves
-		 * from wait queue
-		 */
-		spin_unlock_irqrestore(&q->lock, flags);
-		cpu_relax();
-		spin_lock_irqsave(&q->lock, flags);
-		__wake_up_locked_key_bookmark(q, TASK_NORMAL, &key, &bookmark);
-	}
+	__wake_up_locked_key(q, TASK_NORMAL, &key);
 
 	/*
 	 * It's possible to miss clearing waiters here, when we woke our page
-- 
2.40.1