On Sat, Sep 19, 2009 at 01:52:52AM +0800, Theodore Tso wrote:
> On Fri, Sep 11, 2009 at 10:39:29PM +0800, Wu Fengguang wrote:
> >
> > That would be good. Sorry for the late work. I'll allocate some time
> > in mid next week to help review and benchmark recent writeback works,
> > and hope to get things done in this merge window.
>
> Did you have some chance to get more work done on the your writeback
> patches?
Sorry for the delay, I'm now testing the patches with commands
cp /dev/zero /mnt/test/zero0 &
dd if=/dev/zero of=/mnt/test/zero1 &
and the attached debug patch.
One problem I found with ext3/4 is, redirty_tail() is called repeatedly
in the traces, which could slow down the inode writeback significantly.
Ideal is to call requeue_[partial_]io() instead of redirty_tail().
[ 131.963885] fs/fs-writeback.c +809 wb_writeback(): comm=flush-8:0 pid=2816 n=0
[ 131.966171] global dirty=4105 writeback=18793 nfs=0 flags=__ towrite=32768 skipped=0 file=0 written=0
[ 132.780826] fs/fs-writeback.c +809 wb_writeback(): comm=flush-0:15 pid=1150 n=0
[ 132.783097] global dirty=4105 writeback=16623 nfs=0 flags=__ towrite=32768 skipped=0 file=0 written=0
[ 134.307094] redirty_tail() +542: inode=12
[ 134.815776] redirty_tail() +542: inode=13
[ 134.817709] fs/fs-writeback.c +809 wb_writeback(): comm=flush-8:0 pid=2816 n=11493
[ 134.821242] global dirty=4192 writeback=16203 nfs=0 flags=__ towrite=21275 skipped=0 file=13 written=4430
[ 135.599954] redirty_tail() +542: inode=12
[ 136.372523] redirty_tail() +542: inode=13
[ 136.386748] fs/fs-writeback.c +809 wb_writeback(): comm=flush-8:0 pid=2816 n=11570
[ 136.432168] global dirty=4308 writeback=15752 nfs=0 flags=__ towrite=21198 skipped=0 file=13 written=4650
[ 137.789115] fs/fs-writeback.c +809 wb_writeback(): comm=flush-0:15 pid=1150 n=0
[ 138.587178] global dirty=9551 writeback=10755 nfs=0 flags=__ towrite=32768 skipped=0 file=0 written=0
[ 138.962743] redirty_tail() +542: inode=12
[ 139.395024] redirty_tail() +542: inode=13
[ 139.403194] fs/fs-writeback.c +809 wb_writeback(): comm=flush-8:0 pid=2816 n=11893
[ 139.413026] global dirty=4101 writeback=16630 nfs=0 flags=__ towrite=20875 skipped=0 file=0 written=2
[ 139.426074] fs/fs-writeback.c +809 wb_writeback(): comm=flush-8:0 pid=2816 n=0
[ 139.435190] global dirty=4101 writeback=16378 nfs=0 flags=__ towrite=32768 skipped=0 file=0 written=0
[ 140.266713] redirty_tail() +542: inode=12
[ 140.449304] redirty_tail() +542: inode=13
[ 140.496241] fs/fs-writeback.c +809 wb_writeback(): comm=flush-8:0 pid=2816 n=11678
[ 140.508339] global dirty=4203 writeback=19220 nfs=0 flags=__ towrite=21090 skipped=0 file=13 written=4254
[ 141.649192] redirty_tail() +542: inode=12
[ 141.971276] redirty_tail() +542: inode=13
[ 141.988572] fs/fs-writeback.c +809 wb_writeback(): comm=flush-8:0 pid=2816 n=11304
[ 142.000107] global dirty=4112 writeback=18362 nfs=0 flags=__ towrite=21464 skipped=0 file=13 written=4541
btrfs pattern is almost the same, but with an extra (metadata) inode 1.
[ 464.443873] fs/fs-writeback.c +809 wb_writeback(): comm=flush-btrfs-1 pid=2865 n=0
[ 464.450458] global dirty=163 writeback=4375 nfs=0 flags=__ towrite=32768 skipped=0 file=0 written=0
[ 464.655999] fs/fs-writeback.c +809 wb_writeback(): comm=flush-8:0 pid=2816 n=0
[ 464.664478] global dirty=3873 writeback=1175 nfs=0 flags=__ towrite=32768 skipped=0 file=0 written=0
[ 465.291059] redirty_tail() +542: inode=257
[ 465.331584] redirty_tail() +542: inode=258
[ 465.346433] redirty_tail() +560: inode=1
[ 465.352016] fs/fs-writeback.c +809 wb_writeback(): comm=flush-btrfs-1 pid=2865 n=14480
[ 465.355797] global dirty=337 writeback=3980 nfs=0 flags=__ towrite=18288 skipped=0 file=1 written=0
[ 466.226489] redirty_tail() +542: inode=257
[ 466.280894] redirty_tail() +542: inode=258
[ 466.282270] redirty_tail() +560: inode=1
[ 466.288079] fs/fs-writeback.c +809 wb_writeback(): comm=flush-btrfs-1 pid=2865 n=14300
[ 466.291738] global dirty=666 writeback=3807 nfs=0 flags=__ towrite=18468 skipped=0 file=1 written=0
[ 467.101730] redirty_tail() +542: inode=257
[ 467.134303] redirty_tail() +542: inode=258
[ 467.135675] redirty_tail() +560: inode=1
[ 467.144120] fs/fs-writeback.c +809 wb_writeback(): comm=flush-btrfs-1 pid=2865 n=14032
[ 467.147302] global dirty=331 writeback=3665 nfs=0 flags=__ towrite=18736 skipped=0 file=1 written=0
[ 467.964652] redirty_tail() +542: inode=257
[ 468.002423] redirty_tail() +542: inode=258
[ 468.003795] redirty_tail() +560: inode=1
I'm looking into it.
Thanks,
Fengguang
fs/fs-writeback.c | 30 +++++++++++++++++++++++++++++-
mm/page-writeback.c | 1 +
2 files changed, 30 insertions(+), 1 deletion(-)
--- linux.orig/mm/page-writeback.c 2009-09-19 10:51:09.000000000 +0800
+++ linux/mm/page-writeback.c 2009-09-19 10:51:47.000000000 +0800
@@ -536,6 +536,7 @@ static void balance_dirty_pages(struct a
pages_written += write_chunk - wbc.nr_to_write;
get_dirty_limits(&background_thresh, &dirty_thresh,
&bdi_thresh, bdi);
+ writeback_debug_report(pages_written, &wbc);
}
/*
--- linux.orig/fs/fs-writeback.c 2009-09-19 10:51:46.000000000 +0800
+++ linux/fs/fs-writeback.c 2009-09-19 10:51:47.000000000 +0800
@@ -68,6 +68,33 @@ enum {
#define WS_USED (1 << WS_USED_B)
#define WS_ONSTACK (1 << WS_ONSTACK_B)
+void print_writeback_control(struct writeback_control *wbc)
+{
+ printk(KERN_DEBUG
+ "global dirty=%lu writeback=%lu nfs=%lu "
+ "flags=%c%c towrite=%ld skipped=%ld "
+ "file=%lu written=%lu\n",
+ global_page_state(NR_FILE_DIRTY),
+ global_page_state(NR_WRITEBACK),
+ global_page_state(NR_UNSTABLE_NFS),
+ wbc->encountered_congestion ? 'C':'_',
+ wbc->more_io ? 'M':'_',
+ wbc->nr_to_write,
+ wbc->pages_skipped,
+ wbc->last_file,
+ wbc->last_file_written);
+}
+
+void __writeback_debug_report(long n, struct writeback_control *wbc,
+ const char *file, int line, const char *func)
+{
+ printk(KERN_DEBUG "%s +%d %s(): comm=%s pid=%d n=%ld\n",
+ file, line, func,
+ current->comm, current->pid,
+ n);
+ print_writeback_control(wbc);
+}
+
static inline bool bdi_work_on_stack(struct bdi_work *work)
{
return test_bit(WS_ONSTACK_B, &work->state);
@@ -302,7 +329,7 @@ static void requeue_io(struct inode *ino
*/
static void requeue_partial_io(struct writeback_control *wbc, struct inode *inode)
{
- if (time_before(wbc->last_file_time + HZ, jiffies) ||
+ if (time_before(wbc->last_file_time + 1000 * HZ, jiffies) ||
wbc->last_file_written == 0 ||
wbc->last_file_written >= MAX_WRITEBACK_PAGES) {
requeue_io(inode);
@@ -749,6 +776,7 @@ static long wb_writeback(struct bdi_writ
args->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write;
+ writeback_debug_report(wrote, &wbc);
/*
* If we ran out of stuff to write, bail unless more_io got set
*/
Subject: track redirty_tail() calls
It helps a lot to know how redirty_tail() are called.
Cc: Ken Chen <kenchen@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Fengguang Wu <wfg@xxxxxxxxxxxxxxxx>
---
fs/fs-writeback.c | 36 +++++++++++++++++++++++++++++++++---
1 file changed, 33 insertions(+), 3 deletions(-)
--- linux.orig/fs/fs-writeback.c 2009-09-19 10:51:47.000000000 +0800
+++ linux/fs/fs-writeback.c 2009-09-19 10:52:03.000000000 +0800
@@ -290,6 +290,21 @@ void bdi_start_writeback(struct backing_
bdi_alloc_queue_work(bdi, &args);
}
+#define redirty_tail(inode) \
+ do { \
+ __redirty_tail(inode, __LINE__); \
+ } while (0)
+
+#define requeue_io(inode) \
+ do { \
+ __requeue_io(inode, __LINE__); \
+ } while (0)
+
+#define requeue_partial_io(wbc, inode) \
+ do { \
+ __requeue_partial_io(wbc, inode, __LINE__); \
+ } while (0)
+
/*
* Redirty an inode: set its when-it-was dirtied timestamp and move it to the
* furthest end of its superblock's dirty-inode list.
@@ -299,7 +314,7 @@ void bdi_start_writeback(struct backing_
* the case then the inode must have been redirtied while it was being written
* out and we don't reset its dirtied_when.
*/
-static void redirty_tail(struct inode *inode)
+static void __redirty_tail(struct inode *inode, int line)
{
struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
@@ -311,23 +326,33 @@ static void redirty_tail(struct inode *i
inode->dirtied_when = jiffies;
}
list_move(&inode->i_list, &wb->b_dirty);
+
+ if (sysctl_dirty_debug) {
+ printk(KERN_DEBUG "redirty_tail() +%d: inode=%lu\n",
+ line, inode->i_ino);
+ }
}
/*
* requeue inode for re-scanning after bdi->b_io list is exhausted.
*/
-static void requeue_io(struct inode *inode)
+static void __requeue_io(struct inode *inode, int line)
{
struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
list_move(&inode->i_list, &wb->b_more_io);
+
+ if (sysctl_dirty_debug) {
+ printk(KERN_DEBUG "requeue_io() +%d: inode=%lu\n",
+ line, inode->i_ino);
+ }
}
/*
* continue io on this inode on next writeback if
* it has not accumulated large enough writeback io chunk
*/
-static void requeue_partial_io(struct writeback_control *wbc, struct inode *inode)
+static void __requeue_partial_io(struct writeback_control *wbc, struct inode *inode, int line)
{
if (time_before(wbc->last_file_time + 1000 * HZ, jiffies) ||
wbc->last_file_written == 0 ||
@@ -337,6 +362,11 @@ static void requeue_partial_io(struct wr
}
list_move_tail(&inode->i_list, &inode_to_bdi(inode)->wb.b_io);
+
+ if (sysctl_dirty_debug) {
+ printk(KERN_DEBUG "requeue_partial_io() +%d: inode=%lu\n",
+ line, inode->i_ino);
+ }
}
static void inode_sync_complete(struct inode *inode)
