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

Andrew Morton
2012-03-08T21:24:19Z

On Thu, 08 Mar 2012 17:59:02 +0800
Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> 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 <xiaoguangrong@linux.vnet.ibm.com>
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 <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

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 */
_