From: lipeifeng <lipeifeng@xxxxxxxx>
The old method will firstly find the space in len(info->length
+ info->align_mask), and get address at the desired alignment.
Sometime, addr would be failed if there are enough
addr space in kernel by above method, e.g., you can't get a
addr sized in 1Mbytes, align_mask 1Mbytes successfully although
there are still (2M-1)bytes space in kernel.
This patch would fix thr problem above by the new method: find the
space in info->length and judge if at the desired info->align_mask
at the same time.
Do a simple test in TIF_32BIT:
- Try to malloc (size:1M align:2M) until allocation fails;
- Try to malloc (size:1M align:1M) and account how to space can be
alloced successfully.
Before optimization: alloced 1.9G+ bytes.
After optimization: alloced 0 bytes.
Signed-off-by: lipeifeng <lipeifeng@xxxxxxxx>
---
mm/mmap.c | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index f61a154..30e33d3 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2002,13 +2002,14 @@ static unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
{
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
- unsigned long length, low_limit, high_limit, gap_start, gap_end;
+ unsigned long length, low_limit, high_limit, gap_start, gap_end, gap_end_tmp;
/* Adjust search length to account for worst case alignment overhead */
length = info->length + info->align_mask;
if (length < info->length)
return -ENOMEM;
+ length = info->length;
/*
* Adjust search limits by the desired length.
* See implementation comment at top of unmapped_area().
@@ -2024,8 +2025,12 @@ static unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
/* Check highest gap, which does not precede any rbtree node */
gap_start = mm->highest_vm_end;
- if (gap_start <= high_limit)
- goto found_highest;
+ if (gap_start <= high_limit) {
+ gap_end_tmp = gap_end - info->length;
+ gap_end_tmp -= (gap_end_tmp - info->align_offset) & info->align_mask;
+ if (gap_end_tmp >= gap_start)
+ goto found_highest;
+ }
/* Check if rbtree root looks promising */
if (RB_EMPTY_ROOT(&mm->mm_rb))
@@ -2053,8 +2058,13 @@ static unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
if (gap_end < low_limit)
return -ENOMEM;
if (gap_start <= high_limit &&
- gap_end > gap_start && gap_end - gap_start >= length)
- goto found;
+ gap_end > gap_start && gap_end - gap_start >= length) {
+ gap_end_tmp = gap_end - info->length;
+ gap_end_tmp -= (gap_end_tmp - info->align_offset) & info->align_mask;
+ if (gap_end_tmp >= gap_start)
+ goto found;
+
+ }
/* Visit left subtree if it looks promising */
if (vma->vm_rb.rb_left) {
--
2.7.4
