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Date: Thu, 8 Oct 2009 12:01:36 +0800
From: Wu Fengguang <fengguang.wu@...el.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Theodore Tso <tytso@....edu>,
Christoph Hellwig <hch@...radead.org>,
Dave Chinner <david@...morbit.com>,
Chris Mason <chris.mason@...cle.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
"Li, Shaohua" <shaohua.li@...el.com>,
Myklebust Trond <Trond.Myklebust@...app.com>,
"jens.axboe@...cle.com" <jens.axboe@...cle.com>,
Jan Kara <jack@...e.cz>, Nick Piggin <npiggin@...e.de>,
"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 18/45] writeback: introduce wait queue for
balance_dirty_pages()
On Thu, Oct 08, 2009 at 10:40:37AM +0800, KAMEZAWA Hiroyuki wrote:
> On Thu, 8 Oct 2009 09:58:22 +0800
> Wu Fengguang <fengguang.wu@...el.com> wrote:
> > On Thu, Oct 08, 2009 at 09:01:59AM +0800, KAMEZAWA Hiroyuki wrote:
> > > IIUC, "iowait" cpustat data was calculated by runqueue->nr_iowait as
> > > == kernel/schec.c
> > > void account_idle_time(cputime_t cputime)
> > > {
> > > struct cpu_usage_stat *cpustat = &kstat_this_cpu.cpustat;
> > > cputime64_t cputime64 = cputime_to_cputime64(cputime);
> > > struct rq *rq = this_rq();
> > >
> > > if (atomic_read(&rq->nr_iowait) > 0)
> > > cpustat->iowait = cputime64_add(cpustat->iowait, cputime64);
> > > else
> > > cpustat->idle = cputime64_add(cpustat->idle, cputime64);
> > > }
> > > ==
> > > Then, for showing "cpu is in iowait", runqueue->nr_iowait should be modified
> > > at some places. In old kernel, congestion_wait() at el did that by calling
> > > io_schedule_timeout().
> > >
> > > How this runqueue->nr_iowait is handled now ?
> >
> > Good question. io_schedule() has an old comment for throttling IO wait:
> >
> > * But don't do that if it is a deliberate, throttling IO wait (this task
> > * has set its backing_dev_info: the queue against which it should throttle)
> > */
> > void __sched io_schedule(void)
> >
> > So it looks both Jens' and this patch behaves right in ignoring the
> > iowait accounting for balance_dirty_pages() :)
> >
> Thank you for clarification.
> Then, hmm, %iotwait (which 'top' shows) didn't work as desgined and we need
> to update throttle_vm_writeout() and some in vmscan.c. Thanks for input.
Thanks, you also reminds me to do io_schedule() in the nfs writeback
wait queue :)
> BTW, I'm glad if I can know "how many threads/ios are throttoled now" per bdi.
Good suggestion. How about this patch?
---
writeback: show per-bdi throttled tasks
All currently throttled tasks will be listed, showing the pages to
writeback for them, and total wait time since blocked.
# cat /debug/bdi/8:0/throttle_list
goal=6144kb waited=32ms
goal=6144kb waited=48ms
CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
---
fs/fs-writeback.c | 1 +
include/linux/backing-dev.h | 2 ++
mm/backing-dev.c | 33 +++++++++++++++++++++++++++++++++
3 files changed, 36 insertions(+)
--- linux.orig/include/linux/backing-dev.h 2009-10-08 11:46:28.000000000 +0800
+++ linux/include/linux/backing-dev.h 2009-10-08 11:47:39.000000000 +0800
@@ -101,6 +101,7 @@ struct backing_dev_info {
#ifdef CONFIG_DEBUG_FS
struct dentry *debug_dir;
struct dentry *debug_stats;
+ struct dentry *debug_throttle;
#endif
};
@@ -116,6 +117,7 @@ struct backing_dev_info {
#define DIRTY_THROTTLE_PAGES_STOP (1 << 22)
struct dirty_throttle_task {
+ unsigned long start_time;
long nr_pages;
struct list_head list;
struct completion complete;
--- linux.orig/mm/backing-dev.c 2009-10-08 11:47:37.000000000 +0800
+++ linux/mm/backing-dev.c 2009-10-08 11:59:06.000000000 +0800
@@ -115,6 +115,23 @@ static int bdi_debug_stats_show(struct s
return 0;
}
+static int bdi_debug_throttle_show(struct seq_file *m, void *v)
+{
+ struct backing_dev_info *bdi = m->private;
+ struct dirty_throttle_task *tt;
+ unsigned long flags;
+
+ spin_lock_irqsave(&bdi->throttle_lock, flags);
+ list_for_each_entry(tt, &bdi->throttle_list, list) {
+ seq_printf(m, "goal=%lukb\twaited=%lums\n",
+ tt->nr_pages << (PAGE_SHIFT - 10),
+ (jiffies - tt->start_time) * 1000 / HZ);
+ }
+ spin_unlock_irqrestore(&bdi->throttle_lock, flags);
+
+ return 0;
+}
+
static int bdi_debug_stats_open(struct inode *inode, struct file *file)
{
return single_open(file, bdi_debug_stats_show, inode->i_private);
@@ -127,15 +144,31 @@ static const struct file_operations bdi_
.release = single_release,
};
+static int bdi_debug_throttle_open(struct inode *inode, struct file *file)
+{
+ return single_open(file, bdi_debug_throttle_show, inode->i_private);
+}
+
+static const struct file_operations bdi_debug_throttle_fops = {
+ .open = bdi_debug_throttle_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = single_release,
+};
+
static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
{
bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
bdi, &bdi_debug_stats_fops);
+ bdi->debug_throttle = debugfs_create_file("throttle_list", 0444,
+ bdi->debug_dir, bdi,
+ &bdi_debug_throttle_fops);
}
static void bdi_debug_unregister(struct backing_dev_info *bdi)
{
+ debugfs_remove(bdi->debug_throttle);
debugfs_remove(bdi->debug_stats);
debugfs_remove(bdi->debug_dir);
}
--- linux.orig/fs/fs-writeback.c 2009-10-08 11:44:27.000000000 +0800
+++ linux/fs/fs-writeback.c 2009-10-08 11:47:39.000000000 +0800
@@ -284,6 +284,7 @@ static void bdi_calc_write_bandwidth(str
void bdi_writeback_wait(struct backing_dev_info *bdi, long nr_pages)
{
struct dirty_throttle_task tt = {
+ .start_time = jiffies,
.nr_pages = nr_pages,
.complete = COMPLETION_INITIALIZER_ONSTACK(tt.complete),
};
--
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