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Message-Id: <20201031200518.4178786-6-harshadshirwadkar@gmail.com>
Date: Sat, 31 Oct 2020 13:05:13 -0700
From: Harshad Shirwadkar <harshadshirwadkar@...il.com>
To: linux-ext4@...r.kernel.org
Cc: tytso@....edu, jack@...e.cz,
Harshad Shirwadkar <harshadshirwadkar@...il.com>
Subject: [PATCH 05/10] jbd2: fix fast commit journalling APIs
This patch adds a few misc fixes for jbd2 fast commit functions.
Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@...il.com>
---
fs/ext4/fast_commit.c | 2 +-
fs/jbd2/commit.c | 9 +++++++++
fs/jbd2/journal.c | 28 +++++++++++++---------------
include/linux/jbd2.h | 10 +++++++---
4 files changed, 30 insertions(+), 19 deletions(-)
diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index 1b62d82b9622..b1ca55c7d32a 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -1134,7 +1134,7 @@ int ext4_fc_commit(journal_t *journal, tid_t commit_tid)
"Fast commit ended with blks = %d, reason = %d, subtid - %d",
nblks, reason, subtid);
if (reason == EXT4_FC_REASON_FC_FAILED)
- return jbd2_fc_end_commit_fallback(journal, commit_tid);
+ return jbd2_fc_end_commit_fallback(journal);
if (reason == EXT4_FC_REASON_FC_START_FAILED ||
reason == EXT4_FC_REASON_INELIGIBLE)
return jbd2_complete_transaction(journal, commit_tid);
diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index 353534403769..2444414ad89e 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -450,6 +450,15 @@ void jbd2_journal_commit_transaction(journal_t *journal)
schedule();
write_lock(&journal->j_state_lock);
finish_wait(&journal->j_fc_wait, &wait);
+ /*
+ * TODO: by blocking fast commits here, we are increasing
+ * fsync() latency slightly. Strictly speaking, we don't need
+ * to block fast commits until the transaction enters T_FLUSH
+ * state. So an optimization is possible where we block new fast
+ * commits here and wait for existing ones to complete
+ * just before we enter T_FLUSH. That way, the existing fast
+ * commits and this full commit can proceed parallely.
+ */
}
write_unlock(&journal->j_state_lock);
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index ea15f55aff5c..368727ef3912 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -734,10 +734,12 @@ int jbd2_fc_begin_commit(journal_t *journal, tid_t tid)
if (!journal->j_stats.ts_tid)
return -EINVAL;
- if (tid <= journal->j_commit_sequence)
+ write_lock(&journal->j_state_lock);
+ if (tid <= journal->j_commit_sequence) {
+ write_unlock(&journal->j_state_lock);
return -EALREADY;
+ }
- write_lock(&journal->j_state_lock);
if (journal->j_flags & JBD2_FULL_COMMIT_ONGOING ||
(journal->j_flags & JBD2_FAST_COMMIT_ONGOING)) {
DEFINE_WAIT(wait);
@@ -777,13 +779,19 @@ static int __jbd2_fc_end_commit(journal_t *journal, tid_t tid, bool fallback)
int jbd2_fc_end_commit(journal_t *journal)
{
- return __jbd2_fc_end_commit(journal, 0, 0);
+ return __jbd2_fc_end_commit(journal, 0, false);
}
EXPORT_SYMBOL(jbd2_fc_end_commit);
-int jbd2_fc_end_commit_fallback(journal_t *journal, tid_t tid)
+int jbd2_fc_end_commit_fallback(journal_t *journal)
{
- return __jbd2_fc_end_commit(journal, tid, 1);
+ tid_t tid;
+
+ read_lock(&journal->j_state_lock);
+ tid = journal->j_running_transaction ?
+ journal->j_running_transaction->t_tid : 0;
+ read_unlock(&journal->j_state_lock);
+ return __jbd2_fc_end_commit(journal, tid, true);
}
EXPORT_SYMBOL(jbd2_fc_end_commit_fallback);
@@ -865,7 +873,6 @@ int jbd2_fc_get_buf(journal_t *journal, struct buffer_head **bh_out)
int fc_off;
*bh_out = NULL;
- write_lock(&journal->j_state_lock);
if (journal->j_fc_off + journal->j_fc_first < journal->j_fc_last) {
fc_off = journal->j_fc_off;
@@ -874,7 +881,6 @@ int jbd2_fc_get_buf(journal_t *journal, struct buffer_head **bh_out)
} else {
ret = -EINVAL;
}
- write_unlock(&journal->j_state_lock);
if (ret)
return ret;
@@ -887,11 +893,7 @@ int jbd2_fc_get_buf(journal_t *journal, struct buffer_head **bh_out)
if (!bh)
return -ENOMEM;
- lock_buffer(bh);
- clear_buffer_uptodate(bh);
- set_buffer_dirty(bh);
- unlock_buffer(bh);
journal->j_fc_wbuf[fc_off] = bh;
*bh_out = bh;
@@ -909,9 +911,7 @@ int jbd2_fc_wait_bufs(journal_t *journal, int num_blks)
struct buffer_head *bh;
int i, j_fc_off;
- read_lock(&journal->j_state_lock);
j_fc_off = journal->j_fc_off;
- read_unlock(&journal->j_state_lock);
/*
* Wait in reverse order to minimize chances of us being woken up before
@@ -939,9 +939,7 @@ int jbd2_fc_release_bufs(journal_t *journal)
struct buffer_head *bh;
int i, j_fc_off;
- read_lock(&journal->j_state_lock);
j_fc_off = journal->j_fc_off;
- read_unlock(&journal->j_state_lock);
/*
* Wait in reverse order to minimize chances of us being woken up before
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 9b4e87a0068b..df1285da7276 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -946,7 +946,9 @@ struct journal_s
* @j_fc_off:
*
* Number of fast commit blocks currently allocated.
- * [j_state_lock].
+ * [j_state_lock]. During the commit path, this variable is not
+ * protected by j_state_lock since only one process performs commit
+ * at a time.
*/
unsigned long j_fc_off;
@@ -1110,7 +1112,9 @@ struct journal_s
/**
* @j_fc_wbuf: Array of fast commit bhs for
- * jbd2_journal_commit_transaction.
+ * jbd2_journal_commit_transaction. During the commit path, this
+ * variable is not protected by j_state_lock since only one process
+ * performs commit at a time.
*/
struct buffer_head **j_fc_wbuf;
@@ -1618,7 +1622,7 @@ extern int jbd2_cleanup_journal_tail(journal_t *);
int jbd2_fc_init(journal_t *journal);
int jbd2_fc_begin_commit(journal_t *journal, tid_t tid);
int jbd2_fc_end_commit(journal_t *journal);
-int jbd2_fc_end_commit_fallback(journal_t *journal, tid_t tid);
+int jbd2_fc_end_commit_fallback(journal_t *journal);
int jbd2_fc_get_buf(journal_t *journal, struct buffer_head **bh_out);
int jbd2_submit_inode_data(struct jbd2_inode *jinode);
int jbd2_wait_inode_data(journal_t *journal, struct jbd2_inode *jinode);
--
2.29.1.341.ge80a0c044ae-goog
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