linux-kernel - Re: [PATCH v3] mm: simplify find_vma

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20111212132616.GB15249@tiehlicka.suse.cz>
Date:	Mon, 12 Dec 2011 14:26:16 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	kosaki.motohiro@...il.com
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Shaohua Li <shaohua.li@...el.com>
Subject: Re: [PATCH v3] mm: simplify find_vma_prev

On Fri 09-12-11 17:48:40, kosaki.motohiro@...il.com wrote:
> From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> 
> commit 297c5eee37 (mm: make the vma list be doubly linked) added
> vm_prev member into vm_area_struct. Therefore we can simplify
> find_vma_prev() by using it. Also, this change help to improve
> page fault performance because it has strong locality of reference.
> 
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> ---
>  mm/mmap.c |   36 ++++++++----------------------------
>  1 files changed, 8 insertions(+), 28 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index eae90af..b9c0241 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1603,39 +1603,19 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
>  
>  EXPORT_SYMBOL(find_vma);
>  
> -/* Same as find_vma, but also return a pointer to the previous VMA in *pprev. */
> +/*
> + * Same as find_vma, but also return a pointer to the previous VMA in *pprev.
> + * Note: pprev is set to NULL when return value is NULL.
> + */
>  struct vm_area_struct *
>  find_vma_prev(struct mm_struct *mm, unsigned long addr,
>  			struct vm_area_struct **pprev)
>  {
> -	struct vm_area_struct *vma = NULL, *prev = NULL;
> -	struct rb_node *rb_node;
> -	if (!mm)
> -		goto out;
> -
> -	/* Guard against addr being lower than the first VMA */
> -	vma = mm->mmap;

Why have you removed this guard? Previously we had pprev==NULL and
returned mm->mmap.
This seems like a semantic change without any explanation. Could you
clarify?

> -
> -	/* Go through the RB tree quickly. */
> -	rb_node = mm->mm_rb.rb_node;
> -
> -	while (rb_node) {
> -		struct vm_area_struct *vma_tmp;
> -		vma_tmp = rb_entry(rb_node, struct vm_area_struct, vm_rb);
> -
> -		if (addr < vma_tmp->vm_end) {
> -			rb_node = rb_node->rb_left;
> -		} else {
> -			prev = vma_tmp;
> -			if (!prev->vm_next || (addr < prev->vm_next->vm_end))
> -				break;
> -			rb_node = rb_node->rb_right;
> -		}
> -	}
> +	struct vm_area_struct *vma;
>  
> -out:
> -	*pprev = prev;
> -	return prev ? prev->vm_next : vma;
> +	vma = find_vma(mm, addr);
> +	*pprev = vma ? vma->vm_prev : NULL;
> +	return vma;
>  }
>  
>  /*
> -- 
> 1.7.1
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@...ck.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
> Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a>

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/