[PATCH 1/2] jbd2: Avoid pointless scanning of checkpoint lists

Jan Kara
2014-10-10T14:24:11Z

Yuanhan has reported that when he is running fsync(2) heavy workload
creating new files over ramdisk, significant amount of time is spent in
__jbd2_journal_clean_checkpoint_list() trying to clean old transactions
(but they cannot be cleaned up because flusher hasn't yet checkpointed
those buffers). The workload can be generated by:
fs_mark -d /fs/ram0/1 -D 2 -N 2560 -n 1000000 -L 1 -S 1 -s 4096

Reduce the amount of scanning by stopping to scan the transaction list
once we find a transaction that cannot be checkpointed. Note that this
way of cleaning is still enough to keep freeing space in the journal
after fully checkpointed transactions.

Reported-and-tested-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
fs/jbd2/checkpoint.c | 32 ++++++++++++++++++--------------
1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index 7f34f4716165..e39b2d0e1079 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -478,7 +478,6 @@ int jbd2_cleanup_journal_tail(journal_t *journal)
* Find all the written-back checkpoint buffers in the given list and
* release them.
*
- * Called with the journal locked.
* Called with j_list_lock held.
* Returns number of buffers reaped (for debug)
*/
@@ -498,12 +497,12 @@ static int journal_clean_one_cp_list(struct journal_head *jh, int *released)
jh = next_jh;
next_jh = jh->b_cpnext;
ret = __try_to_free_cp_buf(jh);
- if (ret) {
- freed++;
- if (ret == 2) {
- *released = 1;
- return freed;
- }
+ if (!ret)
+ return freed;
+ freed++;
+ if (ret == 2) {
+ *released = 1;
+ return freed;
}
/*
* This function only frees up some memory
@@ -523,7 +522,6 @@ static int journal_clean_one_cp_list(struct journal_head *jh, int *released)
*
* Find all the written-back checkpoint buffers in the journal and release them.
*
- * Called with the journal locked.
* Called with j_list_lock held.
* Returns number of buffers reaped (for debug)
*/
@@ -531,7 +529,8 @@ static int journal_clean_one_cp_list(struct journal_head *jh, int *released)
int __jbd2_journal_clean_checkpoint_list(journal_t *journal)
{
transaction_t *transaction, *last_transaction, *next_transaction;
- int ret = 0;
+ int ret;
+ int freed = 0;
int released;

transaction = journal->j_checkpoint_transactions;
@@ -543,17 +542,21 @@ int __jbd2_journal_clean_checkpoint_list(journal_t *journal)
do {
transaction = next_transaction;
next_transaction = transaction->t_cpnext;
- ret += journal_clean_one_cp_list(transaction->
+ ret = journal_clean_one_cp_list(transaction->
t_checkpoint_list, &released);
/*
* This function only frees up some memory if possible so we
* dont have an obligation to finish processing. Bail out if
* preemption requested:
*/
- if (need_resched())
+ if (need_resched()) {
+ freed += ret;
goto out;
- if (released)
+ }
+ if (released) {
+ freed += ret;
continue;
+ }
/*
* It is essential that we are as careful as in the case of
* t_checkpoint_list with removing the buffer from the list as
@@ -561,11 +564,12 @@ int __jbd2_journal_clean_checkpoint_list(journal_t *journal)
*/
ret += journal_clean_one_cp_list(transaction->
t_checkpoint_io_list, &released);
- if (need_resched())
+ freed += ret;
+ if (need_resched() || !ret)
goto out;
} while (transaction != last_transaction);
out:
- return ret;
+ return freed;
}

/*