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From: Kuan-Wei Chiu <visitorckw@gmail.com>
To: richard@nod.at, akpm@linux-foundation.org
Cc: chengzhihao1@huawei.com, hch@infradead.org,
	jserv@ccns.ncku.edu.tw, eleanor15x@gmail.com,
	marscheng@google.com, linux-mtd@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	Kuan-Wei Chiu <visitorckw@gmail.com>
Subject: [PATCH v3 1/2] ubifs: Remove unnecessary cond_resched() from list_sort() compare
Date: Fri, 20 Mar 2026 18:09:37 +0000	[thread overview]
Message-ID: <20260320180938.1827148-2-visitorckw@gmail.com> (raw)
In-Reply-To: <20260320180938.1827148-1-visitorckw@gmail.com>

Historically, UBIFS embedded cond_resched() calls inside its
list_sort() comparison callbacks (data_nodes_cmp, nondata_nodes_cmp,
and replay_entries_cmp) to prevent soft lockups when sorting long
lists.

However, further inspection by Richard Weinberger reveals that these
compare functions are extremely lightweight and do not perform any
blocking MTD I/O. Furthermore, the lists being sorted are strictly
bounded in size:
- In the GC case, the list contains at most the number of nodes that
  fit into a single LEB.
- In the replay case, the list spans across a few LEBs from the UBIFS
  journal, amounting to at most a few thousand elements.

Since the compare functions are called a few thousand times at most,
the overhead of frequent scheduling points is unjustified. Removing the
cond_resched() calls simplifies the comparison logic and reduces
unnecessary context switch checks during the sort.

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
---
 fs/ubifs/gc.c     | 2 --
 fs/ubifs/replay.c | 1 -
 2 files changed, 3 deletions(-)

diff --git a/fs/ubifs/gc.c b/fs/ubifs/gc.c
index 0bf08b7755b8..933c79b5cd6b 100644
--- a/fs/ubifs/gc.c
+++ b/fs/ubifs/gc.c
@@ -109,7 +109,6 @@ static int data_nodes_cmp(void *priv, const struct list_head *a,
 	struct ubifs_info *c = priv;
 	struct ubifs_scan_node *sa, *sb;
 
-	cond_resched();
 	if (a == b)
 		return 0;
 
@@ -153,7 +152,6 @@ static int nondata_nodes_cmp(void *priv, const struct list_head *a,
 	struct ubifs_info *c = priv;
 	struct ubifs_scan_node *sa, *sb;
 
-	cond_resched();
 	if (a == b)
 		return 0;
 
diff --git a/fs/ubifs/replay.c b/fs/ubifs/replay.c
index a9a568f4a868..263045e05cf1 100644
--- a/fs/ubifs/replay.c
+++ b/fs/ubifs/replay.c
@@ -305,7 +305,6 @@ static int replay_entries_cmp(void *priv, const struct list_head *a,
 	struct ubifs_info *c = priv;
 	struct replay_entry *ra, *rb;
 
-	cond_resched();
 	if (a == b)
 		return 0;
 
-- 
2.53.0.959.g497ff81fa9-goog


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http://lists.infradead.org/mailman/listinfo/linux-mtd/

  reply	other threads:[~2026-03-20 18:10 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-03-20 18:09 [PATCH v3 0/2] lib/list_sort: Clean up list_sort() scheduling workarounds Kuan-Wei Chiu
2026-03-20 18:09 ` Kuan-Wei Chiu [this message]
2026-03-21  2:06   ` [PATCH v3 1/2] ubifs: Remove unnecessary cond_resched() from list_sort() compare Zhihao Cheng
2026-03-25  7:18   ` Richard Weinberger
2026-03-20 18:09 ` [PATCH v3 2/2] lib/list_sort: Remove dummy cmp() calls to speed up merge_final() Kuan-Wei Chiu
2026-03-25  5:44   ` Christoph Hellwig
2026-03-21  1:21 ` [PATCH v3 0/2] lib/list_sort: Clean up list_sort() scheduling workarounds Andrew Morton

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