patches/old/filemap-remove-use-of-wait-bookmarks.patch

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Subject: filemap: remove use of wait bookmarks
Date: Tue, 10 Oct 2023 04:58:28 +0100

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.

Link: https://lkml.kernel.org/r/20231010035829.544242-1-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Bin Lai <sclaibin@gmail.com>
Cc: Benjamin Segall <bsegall@google.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>

Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/filemap.c |   21 +--------------------
 1 file changed, 1 insertion(+), 20 deletions(-)

--- a/mm/filemap.c~filemap-remove-use-of-wait-bookmarks
+++ a/mm/filemap.c
@@ -1133,32 +1133,13 @@ static void folio_wake_bit(struct folio
 	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
_