linux-kernel - Re: [PATCH v2] mm/vmscan.c: wrap five parameters into shrink_result for reducing the stack consumption

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Date:	Sat, 14 Jun 2014 11:04:42 +0800
From:	Chen Yucong <slaoub@...il.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, mgorman@...e.de,
	mhocko@...e.cz, riel@...hat.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/vmscan.c: wrap five parameters into shrink_result
 for reducing the stack consumption

On Fri, 2014-06-13 at 12:28 -0400, Johannes Weiner wrote:
> On Fri, Jun 13, 2014 at 01:21:15PM +0800, Chen Yucong wrote:
> > On Thu, 2014-06-12 at 21:40 -0700, Andrew Morton wrote:
> > > On Fri, 13 Jun 2014 12:36:31 +0800 Chen Yucong <slaoub@...il.com> wrote:
> > > 
> > > > @@ -1148,7 +1146,8 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
> > > >  		.priority = DEF_PRIORITY,
> > > >  		.may_unmap = 1,
> > > >  	};
> > > > -	unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
> > > > +	unsigned long ret;
> > > > +	struct shrink_result dummy = { };
> > > 
> > > You didn't like the idea of making this static?
> > Sorry! It's my negligence.
> > If we make dummy static, it can help us save more stack.
> > 
> > without change:  
> > 0xffffffff810aede8 reclaim_clean_pages_from_list []:	184
> > 0xffffffff810aeef8 reclaim_clean_pages_from_list []:	184
> > 
> > with change: struct shrink_result dummy = {};
> > 0xffffffff810aed6c reclaim_clean_pages_from_list []:	152
> > 0xffffffff810aee68 reclaim_clean_pages_from_list []:	152
> > 
> > with change: static struct shrink_result dummy ={};
> > 0xffffffff810aed69 reclaim_clean_pages_from_list []:	120
> > 0xffffffff810aee4d reclaim_clean_pages_from_list []:	120
> 
> FWIW, I copied bloat-o-meter and hacked up a quick comparison tool
> that you can feed two outputs of checkstack.pl for a whole vmlinux and
> it shows you the delta.
> 
> The output for your patch (with the static dummy) looks like this:
> 
> +0/-240 -240
> shrink_inactive_list                         136     112     -24
> shrink_page_list                             208     160     -48
> reclaim_clean_pages_from_list                168       -    -168
> 
> (The stack footprint for reclaim_clean_pages_from_list is actually 96
> after your patch, but checkstack.pl skips frames under 100)
> 
Thanks very much for your comparison tool. Its output is more concise.

thx!
cyc

gcc version 4.7.3 (Gentoo 4.7.3-r1 p1.4, pie-0.5.5)
kernel version 3.15(stable)
Intel(R) Core(TM)2 Duo CPU     T5670  @ 1.80GHz

The output for this patch (with the static dummy) is:

+0/-144 -144
shrink_inactive_list                         152     120     -32
shrink_page_list                             232     184     -48
reclaim_clean_pages_from_list                184     120     -64

-------
gcc version 4.7.2 (Debian 4.7.2-5)
kernel version 3.15(stable)
Intel(R) Core(TM) i5-2320 CPU @ 3.00GHz

The output for this patch (with the static dummy) is:

shrink_inactive_list                         136     120     -16
shrink_page_list                             216     168     -48
reclaim_clean_pages_from_list                184     120     -64


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