On Tue, Nov 22, 2011 at 08:11:27AM +0800, Jan Kara wrote:
> On Mon 21-11-11 21:03:45, Wu Fengguang wrote:
> > When dd in 512bytes, generic_perform_write() calls
> > balance_dirty_pages_ratelimited() 8 times for the same page, but
> > obviously the page is only dirtied once.
> >
> > Fix it by accounting nr_dirtied at page dirty time.
> Well, but after this change, the interface balance_dirty_ratelimited_nr()
> is strange because the argument is only used for per-CPU ratelimiting and
> not for per-task ratelimiting...
Yeah I was vaguely aware of this... and still choose to ignore this
since the patchset looked already forbiddingly large at the time ;)
> So if you do this switch then I'd also
> switch bdp_ratelimits to get consistent results and a clean interface and
> completely kill balance_dirty_pages_ratelimited_nr().
Following your suggestions to change ratelimiting as well :)
I'll do the interface change with a standalone patch.
Thanks,
Fengguang
---
Subject: writeback: fix dirtied pages accounting on sub-page writes
Date: Thu Apr 14 07:52:37 CST 2011
When dd in 512bytes, generic_perform_write() calls
balance_dirty_pages_ratelimited() 8 times for the same page, but
obviously the page is only dirtied once.
Fix it by accounting tsk->nr_dirtied and bdp_ratelimits at page dirty time.
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
mm/page-writeback.c | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)
--- linux-next.orig/mm/page-writeback.c 2011-11-22 16:59:48.000000000 +0800
+++ linux-next/mm/page-writeback.c 2011-11-22 17:12:20.000000000 +0800
@@ -1231,8 +1231,6 @@ void balance_dirty_pages_ratelimited_nr(
if (bdi->dirty_exceeded)
ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
- current->nr_dirtied += nr_pages_dirtied;
-
preempt_disable();
/*
* This prevents one CPU to accumulate too many dirtied pages without
@@ -1243,12 +1241,9 @@ void balance_dirty_pages_ratelimited_nr(
p = &__get_cpu_var(bdp_ratelimits);
if (unlikely(current->nr_dirtied >= ratelimit))
*p = 0;
- else {
- *p += nr_pages_dirtied;
- if (unlikely(*p >= ratelimit_pages)) {
- *p = 0;
- ratelimit = 0;
- }
+ else if (unlikely(*p >= ratelimit_pages)) {
+ *p = 0;
+ ratelimit = 0;
}
/*
* Pick up the dirtied pages by the exited tasks. This avoids lots of
@@ -1743,6 +1738,8 @@ void account_page_dirtied(struct page *p
__inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
task_dirty_inc(current);
task_io_account_write(PAGE_CACHE_SIZE);
+ current->nr_dirtied++;
+ __get_cpu_var(bdp_ratelimits)++;
}
}
EXPORT_SYMBOL(account_page_dirtied);
--
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