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From:   Alexey Lyashkov <alexey.lyashkov@gmail.com>
To:     linux-ext4@vger.kernel.org, Theodore Ts'o <tytso@mit.edu>,
        Andreas Dilger <adilger@dilger.ca>,
        Artem Blagodarenko <artem.blagodarenko@gmail.com>
Cc:     Andrew Perepechko <anserper@ya.ru>,
        Alexey Lyashkov <alexey.lyashkov@gmail.com>
Subject: [PATCH] jbd2: wake up journal waiters in FIFO order, not  LIFO
Date:   Wed,  7 Sep 2022 19:59:59 +0300
Message-Id: <20220907165959.1137482-1-alexey.lyashkov@gmail.com>
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From: Andrew Perepechko <anserper@ya.ru>

LIFO wakeup order is unfair and sometimes leads to a journal
user not being able to get a journal handle for hundreds of
transactions in a row.

FIFO wakeup can make things more fair.

Signed-off-by: Alexey Lyashkov <alexey.lyashkov@gmail.com>
---
 fs/jbd2/commit.c      | 2 +-
 fs/jbd2/transaction.c | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index b2b2bc9b88d9..ec2b55879e3a 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -570,7 +570,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 	journal->j_running_transaction = NULL;
 	start_time = ktime_get();
 	commit_transaction->t_log_start = journal->j_head;
-	wake_up(&journal->j_wait_transaction_locked);
+	wake_up_all(&journal->j_wait_transaction_locked);
 	write_unlock(&journal->j_state_lock);
 
 	jbd2_debug(3, "JBD2: commit phase 2a\n");
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index e1be93ccd81c..6a404ac1c178 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -168,7 +168,7 @@ static void wait_transaction_locked(journal_t *journal)
 	int need_to_start;
 	tid_t tid = journal->j_running_transaction->t_tid;
 
-	prepare_to_wait(&journal->j_wait_transaction_locked, &wait,
+	prepare_to_wait_exclusive(&journal->j_wait_transaction_locked, &wait,
 			TASK_UNINTERRUPTIBLE);
 	need_to_start = !tid_geq(journal->j_commit_request, tid);
 	read_unlock(&journal->j_state_lock);
@@ -194,7 +194,7 @@ static void wait_transaction_switching(journal_t *journal)
 		read_unlock(&journal->j_state_lock);
 		return;
 	}
-	prepare_to_wait(&journal->j_wait_transaction_locked, &wait,
+	prepare_to_wait_exclusive(&journal->j_wait_transaction_locked, &wait,
 			TASK_UNINTERRUPTIBLE);
 	read_unlock(&journal->j_state_lock);
 	/*
@@ -920,7 +920,7 @@ void jbd2_journal_unlock_updates (journal_t *journal)
 	write_lock(&journal->j_state_lock);
 	--journal->j_barrier_count;
 	write_unlock(&journal->j_state_lock);
-	wake_up(&journal->j_wait_transaction_locked);
+	wake_up_all(&journal->j_wait_transaction_locked);
 }
 
 static void warn_dirty_buffer(struct buffer_head *bh)
-- 
2.31.1