linux-kernel - Re: [PATCH 1/4] Simplify and comment on anon_vma re-use for anon_vma

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Date:	Tue, 13 Apr 2010 11:51:38 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Borislav Petkov <bp@...en8.de>, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	sgunderson@...foot.com
Subject: Re: [PATCH 1/4] Simplify and comment on anon_vma re-use for
 anon_vma_prepare()

On Mon, 2010-04-12 at 13:22 -0700, Linus Torvalds wrote:
> +static int anon_vma_compatible(struct vm_area_struct *a, struct vm_area_struct *b)
> +{
> +       return a->vm_end == b->vm_start &&
> +               mpol_equal(vma_policy(a), vma_policy(b)) &&
> +               a->vm_file == b->vm_file &&
> +               !((a->vm_flags ^ b->vm_flags) & ~(VM_READ|VM_WRITE|VM_EXEC)) &&
> +               b->vm_pgoff == a->vm_pgoff + ((b->vm_start - a->vm_start) >> PAGE_SHIFT);
> +} 

Maybe write that as:

static int anon_vma_compatible(struct vm_area_struct *a, struct vm_area_struct *b)
{
	if (a->vm_end != b->vm_start)
		return 0;

	if (!mpol_equal(vma_policy(a), vma_policy(b))
		return 0;

	if (a->vm_file != b->vm_file)
		return 0;

	if ((a->vm_flags ^ b->vm_flags) & ~(VM_READ|VM_WRITE|VM_EXEC))
		return 0;

	if (a->vm_pgoff + ((b->vm_start - a->vm_start) >> PAGE_SHIFT) != b->vm_pgoff)
		return 0;

	return 1;
}


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