linux-kernel - Re: [PATCH -mm] vmscan: make mapped executable pages the first class citizen

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Date:	Sun, 10 May 2009 17:59:17 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>, hannes@...xchg.org,
	peterz@...radead.org, riel@...hat.com,
	linux-kernel@...r.kernel.org, tytso@....edu, linux-mm@...ck.org,
	elladan@...imo.com, npiggin@...e.de, cl@...ux-foundation.org,
	minchan.kim@...il.com
Subject: Re: [PATCH -mm] vmscan: make mapped executable pages the first class 
	citizen

2009/5/9 Alan Cox <alan@...rguk.ukuu.org.uk>:
>> The patch seems reasonable but the changelog and the (non-existent)
>> design documentation could do with a touch-up.
>
> Is it right that I as a user can do things like mmap my database
> PROT_EXEC to get better database numbers by making other
> stuff swap first ?
>
> You seem to be giving everyone a "nice my process up" hack.

How about this?
if priority < DEF_PRIORITY-2, aggressive lumpy reclaim in
shrink_inactive_list() already
reclaim the active page forcely.
then, this patch don't change kernel reclaim policy.

anyway, user process non-changable preventing "nice my process up
hack" seems makes sense to me.

test result:

echo 100 > /proc/sys/vm/dirty_ratio
echo 100 > /proc/sys/vm/dirty_background_ratio
run modified qsbench (use mmap(PROT_EXEC) instead malloc)

           active2active vs active2inactive ratio
before    5:5
after       1:9

please don't ask performance number. I haven't reproduce Wu's patch
improvemnt ;)

Wu, What do you think?

---
 mm/vmscan.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Index: b/mm/vmscan.c
===================================================================
--- a/mm/vmscan.c	2009-05-10 02:40:01.000000000 +0900
+++ b/mm/vmscan.c	2009-05-10 03:33:30.000000000 +0900
@@ -1275,7 +1275,8 @@ static void shrink_active_list(unsigned
 			struct address_space *mapping = page_mapping(page);

 			pgmoved++;
-			if (mapping && test_bit(AS_EXEC, &mapping->flags)) {
+			if (mapping && (priority >= DEF_PRIORITY - 2) &&
+			    test_bit(AS_EXEC, &mapping->flags)) {
 				pga2a++;
 				list_add(&page->lru, &l_active);
 				continue;
--
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