linux-kernel - Re: [PATCH v4] mm: get rid of odd jump labels in find_mergeable_anon

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Date:   Mon, 18 Nov 2019 21:22:35 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     linmiaohe <linmiaohe@...wei.com>
Cc:     akpm@...ux-foundation.org, richardw.yang@...ux.intel.com,
        sfr@...b.auug.org.au, rppt@...ux.ibm.com, jannh@...gle.com,
        steve.capper@....com, catalin.marinas@....com, aarcange@...hat.com,
        walken@...gle.com, dave.hansen@...ux.intel.com,
        tiny.windzz@...il.com, jhubbard@...dia.com, david@...hat.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] mm: get rid of odd jump labels in
 find_mergeable_anon_vma()

On Mon, Nov 18, 2019 at 08:24:04PM +0800, linmiaohe wrote:
>From: Miaohe Lin <linmiaohe@...wei.com>
>
>The jump labels try_prev and none are not really needed
>in find_mergeable_anon_vma(), eliminate them to improve
>readability.
>
>Reviewed-by: David Hildenbrand <david@...hat.com>
>Reviewed-by: John Hubbard <jhubbard@...dia.com>
>Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>

Reviewed-by: Wei Yang <richardw.yang@...ux.intel.com>

>---
>-v2:
>	Fix commit descriptions and further simplify the code
>	as suggested by David Hildenbrand and John Hubbard.
>-v3:
>	Rewrite patch version info. Don't show this in commit log.
>-v4:
>	Get rid of var near completely as well.
>---
> mm/mmap.c | 36 ++++++++++++++++--------------------
> 1 file changed, 16 insertions(+), 20 deletions(-)
>
>diff --git a/mm/mmap.c b/mm/mmap.c
>index 91d5e097a4ed..4d93bda30eac 100644
>--- a/mm/mmap.c
>+++ b/mm/mmap.c
>@@ -1273,26 +1273,22 @@ static struct anon_vma *reusable_anon_vma(struct vm_area_struct *old, struct vm_
>  */
> struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma)
> {
>-	struct anon_vma *anon_vma;
>-	struct vm_area_struct *near;
>-
>-	near = vma->vm_next;
>-	if (!near)
>-		goto try_prev;
>-
>-	anon_vma = reusable_anon_vma(near, vma, near);
>-	if (anon_vma)
>-		return anon_vma;
>-try_prev:
>-	near = vma->vm_prev;
>-	if (!near)
>-		goto none;
>-
>-	anon_vma = reusable_anon_vma(near, near, vma);
>-	if (anon_vma)
>-		return anon_vma;
>-none:
>+	struct anon_vma *anon_vma = NULL;
>+
>+	/* Try next first. */
>+	if (vma->vm_next) {
>+		anon_vma = reusable_anon_vma(vma->vm_next, vma, vma->vm_next);
>+		if (anon_vma)
>+			return anon_vma;
>+	}
>+
>+	/* Try prev next. */
>+	if (vma->vm_prev)
>+		anon_vma = reusable_anon_vma(vma->vm_prev, vma->vm_prev, vma);
>+
> 	/*
>+	 * We might reach here with anon_vma == NULL if we can't find
>+	 * any reusable anon_vma.
> 	 * There's no absolute need to look only at touching neighbours:
> 	 * we could search further afield for "compatible" anon_vmas.
> 	 * But it would probably just be a waste of time searching,
>@@ -1300,7 +1296,7 @@ struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma)
> 	 * We're trying to allow mprotect remerging later on,
> 	 * not trying to minimize memory used for anon_vmas.
> 	 */
>-	return NULL;
>+	return anon_vma;
> }
> 
> /*
>-- 
>2.21.GIT

-- 
Wei Yang
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