linux-kernel - Re: [PATCH 1/2] mm: use list.h for vma list

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Message-ID: <20090311105210.GB2282@elte.hu>
Date:	Wed, 11 Mar 2009 11:52:10 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	Daniel Lowengrub <lowdanie@...il.com>, linux-mm@...ck.org,
	a.p.zijlstra@...llo.nl, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: use list.h for vma list


* Alexey Dobriyan <adobriyan@...il.com> wrote:

> On Wed, Mar 11, 2009 at 11:55:48AM +0200, Daniel Lowengrub wrote:
> > Use the linked list defined list.h for the list of vmas that's stored
> > in the mm_struct structure.  Wrapper functions "vma_next" and
> > "vma_prev" are also implemented.  Functions that operate on more than
> > one vma are now given a list of vmas as input.
> 
> > Signed-off-by: Daniel Lowengrub
> 
> That's not how S-o-b line should look like.
> 
> > --- linux-2.6.28.7.vanilla/arch/alpha/kernel/osf_sys.c
> > +++ linux-2.6.28.7/arch/alpha/kernel/osf_sys.c
> > @@ -1197,7 +1197,7 @@
> >  		if (!vma || addr + len <= vma->vm_start)
> >  			return addr;
> >  		addr = vma->vm_end;
> > -		vma = vma->vm_next;
> > +		vma = vma_next(vma);
> 
> Well, this bloats both mm_struct and vm_area_struct.

here's some hard numbers from an earlier submission:

| I made a script that runs 'time ./mmap-perf' 100 times and 
| outputs the average.
|
| The output on the standard kernel was:
|
|   real: 1.022600
|   user: 0.135900
| system: 0.852600
|
| The output after the patch was:
|
|   real: 0.815400
|   user: 0.113200
| system: 0.622200

Which is a 25% speedup in MM performance - which looks very 
significant.

Note: i have not repeated the measurements, and it still looks a 
bit too good - i'd have expected if there's such a low hanging 
25% fruit in the MM we'd have fixed it already.

( Daniel - please preserve such measurements in changelogs. )

	Ingo
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