Jan Kara pointed out that if there is an inode which is constantly
getting dirtied with I_DIRTY_PAGES, an inode with an updated timestamp
will never be written since inode->dirtied_when is constantly getting
updated. We fix this by adding an extra field to the inode,
dirtied_time_when, so inodes with a stale dirtytime can get detected
and handled.
In addition, if we have a dirtytime inode caused by an atime update,
and there is no write activity on the file system, we need to have a
secondary system to make sure these inodes get written out. We do
this by setting up a second delayed work structure which wakes up the
CPU much more rarely compared to writeback_expire_centisecs.
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
---
fs/fs-writeback.c | 82 +++++++++++++++++++++++++++++++++++++++++++++++-------
include/linux/fs.h | 1 +
2 files changed, 73 insertions(+), 10 deletions(-)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index e907052..2cfcd74 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -53,6 +53,18 @@ struct wb_writeback_work {
struct completion *done; /* set if the caller waits */
};
+/*
+ * If an inode is constantly having its pages dirtied, but then the
+ * updates stop dirtytime_expire_interval seconds in the past, it's
+ * possible for the worst case time between when an inode has its
+ * timestamps updated and when they finally get written out to be two
+ * dirtytime_expire_intervals. We set the default to 12 hours (in
+ * seconds), which means most of the time inodes will have their
+ * timestamps written to disk after 12 hours, but in the worst case a
+ * few inodes might not their timestamps updated for 24 hours.
+ */
+unsigned int dirtytime_expire_interval = 12 * 60 * 60;
+
/**
* writeback_in_progress - determine whether there is writeback in progress
* @bdi: the device's backing_dev_info structure.
@@ -275,8 +287,8 @@ static int move_expired_inodes(struct list_head *delaying_queue,
if ((flags & EXPIRE_DIRTY_ATIME) == 0)
older_than_this = work->older_than_this;
- else if ((work->reason == WB_REASON_SYNC) == 0) {
- expire_time = jiffies - (HZ * 86400);
+ else if (!work->for_sync) {
+ expire_time = jiffies - (dirtytime_expire_interval * HZ);
older_than_this = &expire_time;
}
while (!list_empty(delaying_queue)) {
@@ -458,6 +470,7 @@ static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
*/
redirty_tail(inode, wb);
} else if (inode->i_state & I_DIRTY_TIME) {
+ inode->dirtied_when = jiffies;
list_move(&inode->i_wb_list, &wb->b_dirty_time);
} else {
/* The inode is clean. Remove from writeback lists. */
@@ -505,12 +518,17 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
spin_lock(&inode->i_lock);
dirty = inode->i_state & I_DIRTY;
- if (((dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) &&
- (inode->i_state & I_DIRTY_TIME)) ||
- (inode->i_state & I_DIRTY_TIME_EXPIRED)) {
- dirty |= I_DIRTY_TIME | I_DIRTY_TIME_EXPIRED;
- trace_writeback_lazytime(inode);
- }
+ if (inode->i_state & I_DIRTY_TIME) {
+ if ((dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) ||
+ unlikely(inode->i_state & I_DIRTY_TIME_EXPIRED) ||
+ unlikely(time_after(jiffies,
+ (inode->dirtied_time_when +
+ dirtytime_expire_interval * HZ)))) {
+ dirty |= I_DIRTY_TIME | I_DIRTY_TIME_EXPIRED;
+ trace_writeback_lazytime(inode);
+ }
+ } else
+ inode->i_state &= ~I_DIRTY_TIME_EXPIRED;
inode->i_state &= ~dirty;
/*
@@ -1131,6 +1149,45 @@ void wakeup_flusher_threads(long nr_pages, enum wb_reason reason)
rcu_read_unlock();
}
+/*
+ * Wake up bdi's periodically to make sure dirtytime inodes gets
+ * written back periodically. We deliberately do *not* check the
+ * b_dirtytime list in wb_has_dirty_io(), since this would cause the
+ * kernel to be constantly waking up once there are any dirtytime
+ * inodes on the system. So instead we define a separate delayed work
+ * function which gets called much more rarely. (By default, only
+ * once every 12 hours.)
+ *
+ * If there is any other write activity going on in the file system,
+ * this function won't be necessary. But if the only thing that has
+ * happened on the file system is a dirtytime inode caused by an atime
+ * update, we need this infrastructure below to make sure that inode
+ * eventually gets pushed out to disk.
+ */
+static void wakeup_dirtytime_writeback(struct work_struct *w);
+static DECLARE_DELAYED_WORK(dirtytime_work, wakeup_dirtytime_writeback);
+
+static void wakeup_dirtytime_writeback(struct work_struct *w)
+{
+ struct backing_dev_info *bdi;
+
+ rcu_read_lock();
+ list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
+ if (list_empty(&bdi->wb.b_dirty_time))
+ continue;
+ bdi_wakeup_thread(bdi);
+ }
+ rcu_read_unlock();
+ schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
+}
+
+static int __init start_dirtytime_writeback(void)
+{
+ schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
+ return 0;
+}
+__initcall(start_dirtytime_writeback);
+
static noinline void block_dump___mark_inode_dirty(struct inode *inode)
{
if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
@@ -1269,8 +1326,13 @@ void __mark_inode_dirty(struct inode *inode, int flags)
}
inode->dirtied_when = jiffies;
- list_move(&inode->i_wb_list, dirtytime ?
- &bdi->wb.b_dirty_time : &bdi->wb.b_dirty);
+ if (dirtytime)
+ inode->dirtied_time_when = jiffies;
+ if (inode->i_state & (I_DIRTY_INODE | I_DIRTY_PAGES))
+ list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
+ else
+ list_move(&inode->i_wb_list,
+ &bdi->wb.b_dirty_time);
spin_unlock(&bdi->wb.list_lock);
trace_writeback_dirty_inode_enqueue(inode);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b4d71b5..f4131e8 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -604,6 +604,7 @@ struct inode {
struct mutex i_mutex;
unsigned long dirtied_when; /* jiffies of first dirtying */
+ unsigned long dirtied_time_when;
struct hlist_node i_hash;
struct list_head i_wb_list; /* backing dev IO list */
--
2.3.0
--
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