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

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Date:	Sun, 10 May 2009 17:20:53 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"riel@...hat.com" <riel@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tytso@....edu" <tytso@....edu>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"elladan@...imo.com" <elladan@...imo.com>,
	"npiggin@...e.de" <npiggin@...e.de>,
	"cl@...ux-foundation.org" <cl@...ux-foundation.org>,
	"minchan.kim@...il.com" <minchan.kim@...il.com>
Subject: Re: [PATCH -mm] vmscan: make mapped executable pages the first
	class  citizen

On Sun, May 10, 2009 at 04:59:17PM +0800, KOSAKI Motohiro wrote:
> 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?

Why it deserves more tricks? PROT_EXEC pages are rare.
If user space is to abuse PROT_EXEC, let them be for it ;-)

> if priority < DEF_PRIORITY-2, aggressive lumpy reclaim in
> shrink_inactive_list() already
> reclaim the active page forcely.

Isn't lumpy reclaim now enabled by (and only by) non-zero order?

> 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

Do you have scripts for producing such numbers? I'm dreaming to have
such tools :-)

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

That's why I decided to "explain" instead of "benchmark" the benefits
of my patch, hehe.

Thanks,
Fengguang

> ---
>  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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