Subject: Re: linux-next: manual merge of the akpm tree with Linus' tree

From: Andrew Morton <[email-masked]>
Date: Thu, 8 Mar 2012 13:24:15 -0800

On Thu, 08 Mar 2012 17:59:02 +0800
Xiao Guangrong <[email-masked]> wrote:

> Andrew, the patch has been reworked.
> 
> Subject: [PATCH] hugetlb: drop prev_vma in hugetlb_get_unmapped_area_topdown()
> 
> After the call find_vma_prev(mm, addr, &prev_vma), the following condition
> is always true:
> 
> 	!prev_vma || (addr >= prev_vma->vm_end)
> 
> it can happily drop prev_vma and use find_vma() instead of find_vma_prev().
> 

Well OK, but the changelog is wrong - we don't call find_vma_prev()
here any more.

How does this look?

From: Xiao Guangrong <[email-masked]>
Subject: hugetlb: remove prev_vma from hugetlb_get_unmapped_area_topdown()

After looking up the vma which covers or follows the cached search
address, the following condition is always true:

	!prev_vma || (addr >= prev_vma->vm_end)

so we can stop checking the previous VMA altogether.

Signed-off-by: Xiao Guangrong <[email-masked]>
Signed-off-by: Andrew Morton <[email-masked]>
---

 arch/x86/mm/hugetlbpage.c |   18 +++++-------------
 1 file changed, 5 insertions(+), 13 deletions(-)

diff -puN arch/x86/mm/hugetlbpage.c~hugetlb-drop-prev_vma-in-hugetlb_get_unmapped_area_topdown arch/x86/mm/hugetlbpage.c
--- a/arch/x86/mm/hugetlbpage.c~hugetlb-drop-prev_vma-in-hugetlb_get_unmapped_area_topdown
+++ a/arch/x86/mm/hugetlbpage.c
@@ -308,7 +308,7 @@ static unsigned long hugetlb_get_unmappe
 {
 	struct hstate *h = hstate_file(file);
 	struct mm_struct *mm = current->mm;
-	struct vm_area_struct *vma, *prev_vma;
+	struct vm_area_struct *vma;
 	unsigned long base = mm->mmap_base;
 	unsigned long addr = addr0;
 	unsigned long largest_hole = mm->cached_hole_size;
@@ -340,22 +340,14 @@ try_again:
 		if (!vma)
 			return addr;
 
-		/*
-		 * new region fits between prev_vma->vm_end and
-		 * vma->vm_start, use it:
-		 */
-		prev_vma = vma->vm_prev;
-		if (addr + len <= vma->vm_start &&
-		            (!prev_vma || (addr >= prev_vma->vm_end))) {
+		if (addr + len <= vma->vm_start) {
 			/* remember the address as a hint for next time */
 		        mm->cached_hole_size = largest_hole;
 		        return (mm->free_area_cache = addr);
-		} else {
+		} else if (mm->free_area_cache == vma->vm_end) {
 			/* pull free_area_cache down to the first hole */
-		        if (mm->free_area_cache == vma->vm_end) {
-				mm->free_area_cache = vma->vm_start;
-				mm->cached_hole_size = largest_hole;
-			}
+			mm->free_area_cache = vma->vm_start;
+			mm->cached_hole_size = largest_hole;
 		}
 
 		/* remember the largest hole we saw so far */
_