Hi Jan,
I believe the following should address all of the issues that you
raised. Could you take a look and let me know what you think?
Thanks!!
- Ted
commit e42f32d0ed65059e5cb689cc0ac28099a729ba9a
Author: Theodore Ts'o <tytso@xxxxxxx>
Date: Sat Mar 7 00:22:37 2015 -0500
fs: make sure the timestamps for lazytime inodes eventually get written
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.
Also add a sysctl tunable, dirtytime_expire_seconds so we can properly
debug this code and make sure it all works.
Finally, 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>
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index e907052..260d7e7 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -53,6 +53,9 @@ struct wb_writeback_work {
struct completion *done; /* set if the caller waits */
};
+/* 12 hours in seconds */
+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 +278,8 @@ 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 +461,7 @@ 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. */
@@ -741,6 +745,13 @@ static long writeback_sb_inodes(struct super_block *sb,
spin_lock(&inode->i_lock);
if (!(inode->i_state & I_DIRTY_ALL))
wrote++;
+ if ((inode->i_state & I_DIRTY_TIME) &&
+ ((start_time - inode->dirtied_time_when) >
+ (dirtytime_expire_interval * HZ))) {
+ inode->i_state &= ~I_DIRTY_TIME;
+ inode->i_state |= I_DIRTY_SYNC;
+ trace_writeback_lazytime(inode);
+ }
requeue_inode(inode, wb, &wbc);
inode_sync_complete(inode);
spin_unlock(&inode->i_lock);
@@ -1131,6 +1142,56 @@ 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.
+ *
+ * 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);
+
+int dirtytime_interval_handler(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ int ret;
+
+ ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+ if (ret == 0 && write)
+ mod_delayed_work(system_wq, &dirtytime_work, 0);
+ return ret;
+}
+
+
static noinline void block_dump___mark_inode_dirty(struct inode *inode)
{
if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
@@ -1269,6 +1330,10 @@ void __mark_inode_dirty(struct inode *inode, int flags)
}
inode->dirtied_when = jiffies;
+ if (dirtytime)
+ inode->dirtied_time_when = jiffies;
+ if (flags & I_DIRTY_PAGES)
+ dirtytime = 0;
list_move(&inode->i_wb_list, dirtytime ?
&bdi->wb.b_dirty_time : &bdi->wb.b_dirty);
spin_unlock(&bdi->wb.list_lock);
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 */
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 0004833..b2dd371e 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -130,6 +130,7 @@ extern int vm_dirty_ratio;
extern unsigned long vm_dirty_bytes;
extern unsigned int dirty_writeback_interval;
extern unsigned int dirty_expire_interval;
+extern unsigned int dirtytime_expire_interval;
extern int vm_highmem_is_dirtyable;
extern int block_dump;
extern int laptop_mode;
@@ -146,6 +147,8 @@ extern int dirty_ratio_handler(struct ctl_table *table, int write,
extern int dirty_bytes_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
loff_t *ppos);
+int dirtytime_interval_handler(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos);
struct ctl_table;
int dirty_writeback_centisecs_handler(struct ctl_table *, int,
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 88ea2d6..ce410bb 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1228,6 +1228,14 @@ static struct ctl_table vm_table[] = {
.extra1 = &zero,
},
{
+ .procname = "dirtytime_expire_seconds",
+ .data = &dirtytime_expire_interval,
+ .maxlen = sizeof(dirty_expire_interval),
+ .mode = 0644,
+ .proc_handler = dirtytime_interval_handler,
+ .extra1 = &zero,
+ },
+ {
.procname = "nr_pdflush_threads",
.mode = 0444 /* read-only */,
.proc_handler = pdflush_proc_obsolete,
--
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