linux-kernel - Re: [RFC] mm: change find

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Date:	Mon, 14 Dec 2015 18:55:09 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	yalin wang <yalin.wang2010@...il.com>, akpm@...ux-foundation.org,
	kirill.shutemov@...ux.intel.com, gang.chen.5i5j@...il.com,
	mhocko@...e.com, kwapulinski.piotr@...il.com, aarcange@...hat.com,
	dcashman@...gle.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] mm: change find_vma() function

On 12/14, Kirill A. Shutemov wrote:
>
> On Mon, Dec 14, 2015 at 07:02:25PM +0800, yalin wang wrote:
> > change find_vma() to break ealier when found the adderss
> > is not in any vma, don't need loop to search all vma.
> >
> > Signed-off-by: yalin wang <yalin.wang2010@...il.com>
> > ---
> >  mm/mmap.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index b513f20..8294c9b 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -2064,6 +2064,9 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
> >  			vma = tmp;
> >  			if (tmp->vm_start <= addr)
> >  				break;
> > +			if (!tmp->vm_prev || tmp->vm_prev->vm_end <= addr)
> > +				break;
> > +
>
> This 'break' would return 'tmp' as found vma.

But this would be right?

Not that I think this optimization makes sense, I simply do not know,
but to me this change looks technically correct at first glance...

But the changelog is wrong or I missed something. This change can stop
the main loop earlier; if "tmp" is the first vma, or if the previous one
is below the address. Or perhaps I just misread that "not in any vma"
note in the changelog.

No?

Oleg.

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