From: Artem Bityutskiy <Artem.Bityutskiy@xxxxxxxxx>
The 'sync_supers' thread wakes up every 5 seconds (by default) and
writes back all super blocks. It keeps waking up even if there
are no dirty super-blocks. For many file-systems the superblock
becomes dirty very rarely, if ever, so 'sync_supers' does not do
anything most of the time.
This patch improves 'sync_supers' and makes it sleep if all superblocks
are clean and there is nothing to do. This helps saving the power.
This optimization is important for small battery-powered devices.
The locking scheme was provided by Nick Piggin <npiggin@xxxxxxx>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@xxxxxxxxx>
---
include/linux/fs.h | 5 +----
mm/backing-dev.c | 40 ++++++++++++++++++++++++++++++++--------
2 files changed, 33 insertions(+), 12 deletions(-)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 1688464..ca1e993 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1783,10 +1783,7 @@ extern int get_sb_pseudo(struct file_system_type *, char *,
struct vfsmount *mnt);
extern void simple_set_mnt(struct vfsmount *mnt, struct super_block *sb);
-static inline void sb_mark_dirty(struct super_block *sb)
-{
- sb->s_dirty = 1;
-}
+void sb_mark_dirty(struct super_block *sb);
static inline void sb_mark_clean(struct super_block *sb)
{
sb->s_dirty = 0;
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 660a87a..d751284 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -45,6 +45,7 @@ LIST_HEAD(bdi_pending_list);
static struct task_struct *sync_supers_tsk;
static struct timer_list sync_supers_timer;
+static unsigned long supers_dirty __read_mostly;
static int bdi_sync_supers(void *);
static void sync_supers_timer_fn(unsigned long);
@@ -251,7 +252,6 @@ static int __init default_bdi_init(void)
init_timer(&sync_supers_timer);
setup_timer(&sync_supers_timer, sync_supers_timer_fn, 0);
- bdi_arm_supers_timer();
err = bdi_init(&default_backing_dev_info);
if (!err)
@@ -350,6 +350,21 @@ static void bdi_flush_io(struct backing_dev_info *bdi)
writeback_inodes_wbc(&wbc);
}
+void sb_mark_dirty(struct super_block *sb)
+{
+ sb->s_dirty = 1;
+ /*
+ * sb->s_dirty store must be visible to sync_supers before we load
+ * supers_dirty in case we need to re-arm the timer.
+ */
+ smp_mb();
+ if (likely(supers_dirty))
+ return;
+ supers_dirty = 1;
+ bdi_arm_supers_timer();
+}
+EXPORT_SYMBOL_GPL(sb_mark_dirty);
+
/*
* kupdated() used to do this. We cannot do it from the bdi_forker_task()
* or we risk deadlocking on ->s_umount. The longer term solution would be
@@ -362,10 +377,20 @@ static int bdi_sync_supers(void *unused)
while (!kthread_should_stop()) {
set_current_state(TASK_INTERRUPTIBLE);
+ if (supers_dirty)
+ bdi_arm_supers_timer();
schedule();
+ supers_dirty = 0;
/*
- * Do this periodically, like kupdated() did before.
+ * supers_dirty store must be visible to sb_mark_dirty() before
+ * sync_supers runs (which loads ->s_dirty), so a barrier is
+ * needed.
+ */
+ smp_mb();
+ /*
+ * sync_supers() used to do this periodically, but now we
+ * wake up only if there are dirty superblocks.
*/
sync_supers();
}
@@ -373,6 +398,11 @@ static int bdi_sync_supers(void *unused)
return 0;
}
+static void sync_supers_timer_fn(unsigned long unused)
+{
+ wake_up_process(sync_supers_tsk);
+}
+
void bdi_arm_supers_timer(void)
{
unsigned long next;
@@ -384,12 +414,6 @@ void bdi_arm_supers_timer(void)
mod_timer(&sync_supers_timer, round_jiffies_up(next));
}
-static void sync_supers_timer_fn(unsigned long unused)
-{
- wake_up_process(sync_supers_tsk);
- bdi_arm_supers_timer();
-}
-
static int bdi_forker_task(void *ptr)
{
struct bdi_writeback *me = ptr;
--
1.7.0.1
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
