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From: Shaohua Li <shaohua.li@intel.com>
To: Minchan Kim <minchan.kim@gmail.com>
Cc: linux-mm <linux-mm@kvack.org>, Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [patch]vmscan: make kswapd use a correct order
Date: Wed, 01 Dec 2010 13:42:05 +0800	[thread overview]
Message-ID: <1291182125.12777.69.camel@sli10-conroe> (raw)
In-Reply-To: <AANLkTi=whw86_7T0tVi5S8xmwS+Z3PDE_AbXEJSQFqR4@mail.gmail.com>

On Wed, 2010-12-01 at 12:21 +0800, Minchan Kim wrote:
> On Wed, Dec 1, 2010 at 12:08 PM, Shaohua Li <shaohua.li@intel.com> wrote:
> > T0: Task1 wakeup_kswapd(order=3)
> > T1: kswapd enters balance_pgdat
> > T2: Task2 wakeup_kswapd(order=2), because pages reclaimed by kswapd are used
> > quickly
> > T3: kswapd exits balance_pgdat. kswapd will do check. Now new order=2,
> > pgdat->kswapd_max_order will become 0, but order=3, if sleeping_prematurely,
> > then order will become pgdat->kswapd_max_order(0), while at this time the
> > order should 2
> > This isn't a big deal, but we do have a small window the order is wrong.
> >
> > Signed-off-by: Shaohua Li <shaohua.li@intel.com>
> Reviewed-by: Minchan Kim <minchan.kim@gmai.com>
> 
> But you need the description more easily.
> 
> I try it.
Thanks, changed the description.


T0: Task 1 wakes up kswapd with order-3
T1: So, kswapd starts to reclaim pages using balance_pgdat
T2: Task 2 wakes up kswapd with order-2 because pages reclaimed by T1
are consumed quickly.
T3: kswapd exits balance_pgdat and will do following:
T4-1: In beginning of kswapd's loop, pgdat->kswapd_max_order will be
reset with zero.
T4-2: order will be set to pgdat->kswapd_max_order(0), since it enters the
false branch of 'if (order (3) < new_order (2))'
T4-3: If previous balance_pgdat can't meet requirement of order-2 free
pages by high watermark, it will start reclaiming again. So balance_pgdat will
use order-0 to do reclaim, while at this time it really should use order-2

This isn't a big deal, but we do have a small window the order is wrong.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index d31d7ce..c630349 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2450,7 +2450,8 @@ static int kswapd(void *p)
 				}
 			}
 
-			order = pgdat->kswapd_max_order;
+			order = max_t(unsigned long, new_order,
+				pgdat->kswapd_max_order);
 		}
 		finish_wait(&pgdat->kswapd_wait, &wait);
 


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  reply	other threads:[~2010-12-01  5:42 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-12-01  3:08 [patch]vmscan: make kswapd use a correct order Shaohua Li
2010-12-01  4:21 ` Minchan Kim
2010-12-01  5:42   ` Shaohua Li [this message]
2010-12-01  9:44 ` KOSAKI Motohiro
2010-12-01 15:58   ` Minchan Kim
2010-12-02  0:09     ` KOSAKI Motohiro
2010-12-02  0:29       ` KOSAKI Motohiro
2010-12-02  0:58         ` Minchan Kim
2010-12-02  0:19     ` Andrew Morton
2010-12-02  9:40       ` Mel Gorman
2010-12-02  0:29     ` Shaohua Li
2010-12-02  0:54       ` Minchan Kim
2010-12-02  1:05         ` Shaohua Li
2010-12-02  1:23           ` Minchan Kim
2010-12-02  1:36             ` Minchan Kim
2010-12-02  9:42               ` Mel Gorman
2010-12-02 15:25                 ` Minchan Kim
2010-12-02  2:39             ` Shaohua Li
2010-12-02  1:28       ` KOSAKI Motohiro
2010-12-02 10:12     ` Mel Gorman
2010-12-02 15:35       ` Minchan Kim
2010-12-02 15:42         ` Mel Gorman
2010-12-02 20:53           ` Simon Kirby
2010-12-03 12:00             ` Mel Gorman
2010-12-04 12:07               ` Simon Kirby
2010-12-06 12:03                 ` Mel Gorman
2010-12-09 23:44                   ` Simon Kirby
2010-12-10 11:32                     ` Mel Gorman
2010-12-10 23:42                       ` Simon Kirby
2010-12-14  9:52                         ` Mel Gorman
  -- strict thread matches above, loose matches on Subject: below --
2010-12-02 16:00 [PATCH] vmscan: " Minchan Kim
2010-12-03 12:11 ` Mel Gorman
2010-12-09 22:13 ` Andrew Morton
2010-12-10  3:53   ` Minchan Kim
2010-12-10 11:17   ` Mel Gorman

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