linux-kernel - Re: [PATCH -mmotm 3/3] memcg: dirty pages instrumentation

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Date:	Mon, 1 Mar 2010 23:18:31 +0100
From:	Andrea Righi <arighi@...eler.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Greg Thelen <gthelen@...gle.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Andrew Morton <akpm@...ux-foundation.org>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH -mmotm 3/3] memcg: dirty pages instrumentation

On Mon, Mar 01, 2010 at 05:02:08PM -0500, Vivek Goyal wrote:
> > @@ -686,10 +699,14 @@ void throttle_vm_writeout(gfp_t gfp_mask)
> >                   */
> >                  dirty_thresh += dirty_thresh / 10;      /* wheeee... */
> >  
> > -                if (global_page_state(NR_UNSTABLE_NFS) +
> > -			global_page_state(NR_WRITEBACK) <= dirty_thresh)
> > -                        	break;
> > -                congestion_wait(BLK_RW_ASYNC, HZ/10);
> > +
> > +		dirty = mem_cgroup_page_stat(MEMCG_NR_DIRTY_WRITEBACK_PAGES);
> > +		if (dirty < 0)
> > +			dirty = global_page_state(NR_UNSTABLE_NFS) +
> > +				global_page_state(NR_WRITEBACK);
> 
> dirty is unsigned long. As mentioned last time, above will never be true?
> In general these patches look ok to me. I will do some testing with these.

Re-introduced the same bug. My bad. :(

The value returned from mem_cgroup_page_stat() can be negative, i.e.
when memory cgroup is disabled. We could simply use a long for dirty,
the unit is in # of pages so s64 should be enough. Or cast dirty to long
only for the check (see below).

Thanks!
-Andrea

Signed-off-by: Andrea Righi <arighi@...eler.com>
---
 mm/page-writeback.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index d83f41c..dbee976 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -701,7 +701,7 @@ void throttle_vm_writeout(gfp_t gfp_mask)
 
 
 		dirty = mem_cgroup_page_stat(MEMCG_NR_DIRTY_WRITEBACK_PAGES);
-		if (dirty < 0)
+		if ((long)dirty < 0)
 			dirty = global_page_state(NR_UNSTABLE_NFS) +
 				global_page_state(NR_WRITEBACK);
 		if (dirty <= dirty_thresh)
--
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