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 with unmapped_area:
- Try to take addr (size:1M align:2M) until allocation fails;
- Try to take addr (size:1M align:1M) and account how to space can
be alloced successfully.
Before optimization: alloced 0 bytes.
After optimization: alloced 1.9+G bytes.
Signed-off-by: lipeifeng <lipeifeng@xxxxxxxx>
---
mm/mmap.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index a28ea5c..cb002f2 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1923,6 +1923,7 @@ static unsigned long unmapped_area(struct vm_unmapped_area_info *info)
return -ENOMEM;
low_limit = info->low_limit + length;
+ length = info->length;
/* Check if rbtree root looks promising */
if (RB_EMPTY_ROOT(&mm->mm_rb))
goto check_highest;
@@ -1944,6 +1945,8 @@ static unsigned long unmapped_area(struct vm_unmapped_area_info *info)
}
gap_start = vma->vm_prev ? vm_end_gap(vma->vm_prev) : 0;
+ /* Adjust gap address to the desired alignment */
+ gap_start += (info->align_offset - gap_start) & info->align_mask;
check_current:
/* Check if current node has a suitable gap */
if (gap_start > high_limit)
@@ -1984,15 +1987,19 @@ static unsigned long unmapped_area(struct vm_unmapped_area_info *info)
gap_end = ULONG_MAX; /* Only for VM_BUG_ON below */
if (gap_start > high_limit)
return -ENOMEM;
-
+ if (gap_start >= info->low_limit) {
+ gap_start += (info->align_offset - gap_start) & info->align_mask;
+ goto return_gap_start;
+ }
found:
/* We found a suitable gap. Clip it with the original low_limit. */
- if (gap_start < info->low_limit)
+ if (gap_start < info->low_limit) {
gap_start = info->low_limit;
+ /* Adjust gap address to the desired alignment */
+ gap_start += (info->align_offset - gap_start) & info->align_mask;
+ }
- /* Adjust gap address to the desired alignment */
- gap_start += (info->align_offset - gap_start) & info->align_mask;
-
+return_gap_start:
VM_BUG_ON(gap_start + info->length > info->high_limit);
VM_BUG_ON(gap_start + info->length > gap_end);
return gap_start;
--
2.7.4
