linux-kernel - Re: [PATCH] kswapd: avoid unnecessary rebalance after an unsuccessful balancing

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Wed, 03 Aug 2011 08:49:42 +0800
From:	"Alex,Shi" <alex.shi@...el.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"P@...igBrady.com" <P@...igBrady.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"andrea@...share.com" <andrea@...share.com>,
	"Chen, Tim C" <tim.c.chen@...el.com>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"riel@...hat.com" <riel@...hat.com>, "luto@....edu" <luto@....edu>
Subject: Re: [PATCH] kswapd: avoid unnecessary rebalance after an
 unsuccessful balancing


> You're right. I was thinking only of classzone_idx. I see the point now.
> 
> Acked-by: Mel Gorman <mgorman@...e.de>

Thanks for your 'Ack', I want to follow your commit comments and correct
a coding style issue, so I rewrite the patch here.

--------------

In commit 215ddd66, Mel Gorman said kswapd is better to sleep after a
unsuccessful balancing if there is tighter reclaim request pending in
the balancing. But in the following scenario, kswapd do something that
is not matched our expectation. The patch fixes this issue.

1, Read pgdat request A (classzone_idx, order = 3)
2, balance_pgdat()
3,    During pgdat, a new pgdat request B (classzone_idx, order = 5) is
placed
4, balance_pgdat() returns but failed since returned order = 0
5, pgdat of request A assigned to balance_pgdat(), and do balancing
again. While the expectation behavior of kswapd should try to sleep.

Signed-off-by: Alex Shi <alex.shi@...el.com>
Reviewed-by: Tim Chen <tim.c.chen@...ux.intel.com>
Acked-by: Mel Gorman <mgorman@...e.de>
---
 mm/vmscan.c |   14 +++++++++++---
 1 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index eb7bcce..ed8c84c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2792,7 +2792,9 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
 static int kswapd(void *p)
 {
 	unsigned long order, new_order;
+	unsigned balanced_order;
 	int classzone_idx, new_classzone_idx;
+	int balanced_classzone_idx;
 	pg_data_t *pgdat = (pg_data_t*)p;
 	struct task_struct *tsk = current;
 
@@ -2823,7 +2825,9 @@ static int kswapd(void *p)
 	set_freezable();
 
 	order = new_order = 0;
+	balanced_order = 0;
 	classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
+	balanced_classzone_idx = classzone_idx;
 	for ( ; ; ) {
 		int ret;
 
@@ -2832,7 +2836,8 @@ static int kswapd(void *p)
 		 * new request of a similar or harder type will succeed soon
 		 * so consider going to sleep on the basis we reclaimed at
 		 */
-		if (classzone_idx >= new_classzone_idx && order == new_order) {
+		if (balanced_classzone_idx >= new_classzone_idx &&
+					balanced_order == new_order) {
 			new_order = pgdat->kswapd_max_order;
 			new_classzone_idx = pgdat->classzone_idx;
 			pgdat->kswapd_max_order =  0;
@@ -2847,7 +2852,8 @@ static int kswapd(void *p)
 			order = new_order;
 			classzone_idx = new_classzone_idx;
 		} else {
-			kswapd_try_to_sleep(pgdat, order, classzone_idx);
+			kswapd_try_to_sleep(pgdat, balanced_order,
+						balanced_classzone_idx);
 			order = pgdat->kswapd_max_order;
 			classzone_idx = pgdat->classzone_idx;
 			new_order = order;
@@ -2866,7 +2872,9 @@ static int kswapd(void *p)
 		 */
 		if (!ret) {
 			trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
-			order = balance_pgdat(pgdat, order, &classzone_idx);
+			balanced_classzone_idx = classzone_idx;
+			balanced_order = balance_pgdat(pgdat, order,
+						&balanced_classzone_idx);
 		}
 	}
 	return 0;
-- 
1.6.3.3



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/