Re: [PATCH 4/5] writeback: per task dirty rate limit

Wu Fengguang
2011-08-08T14:21:32Z

On Mon, Aug 08, 2011 at 09:47:14PM +0800, Peter Zijlstra wrote:
> On Sat, 2011-08-06 at 16:44 +0800, Wu Fengguang wrote:
> > Add two fields to task_struct.
> >
> > 1) account dirtied pages in the individual tasks, for accuracy
> > 2) per-task balance_dirty_pages() call intervals, for flexibility
> >
> > The balance_dirty_pages() call interval (ie. nr_dirtied_pause) will
> > scale near-sqrt to the safety gap between dirty pages and threshold.
> >
> > XXX: The main problem of per-task nr_dirtied is, if 10k tasks start
> > dirtying pages at exactly the same time, each task will be assigned a
> > large initial nr_dirtied_pause, so that the dirty threshold will be
> > exceeded long before each task reached its nr_dirtied_pause and hence
> > call balance_dirty_pages().
> >
> > Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> > ---
> > include/linux/sched.h | 7 ++
> > mm/memory_hotplug.c | 3 -
> > mm/page-writeback.c | 106 +++++++++-------------------------------
> > 3 files changed, 32 insertions(+), 84 deletions(-)
>
> No fork() hooks? This way tasks inherit their parent's dirty count on
> clone().

Ah good point. Here is the quick fix.

Thanks,
Fengguang
---

--- linux-next.orig/kernel/fork.c 2011-08-08 22:11:59.000000000 +0800
+++ linux-next/kernel/fork.c 2011-08-08 22:18:05.000000000 +0800
@@ -1301,6 +1301,9 @@ static struct task_struct *copy_process(
p->pdeath_signal = 0;
p->exit_state = 0;

+ p->nr_dirtied = 0;
+ p->nr_dirtied_pause = 8;
+
/*
* Ok, make it visible to the rest of the system.
* We dont wake it up yet.