Commit c568da28 authored by Wei Yang's avatar Wei Yang Committed by Linus Torvalds

mm/vmalloc.c: halve the number of comparisons performed in pcpu_get_vm_areas()

In pcpu_get_vm_areas(), it checks each range is not overlapped.  To make
sure it is, only (N^2)/2 comparison is necessary, while current code
does N^2 times.  By starting from the next range, it achieves the goal
and the continue could be removed.

Also,

 - the overlap check of two ranges could be done with one clause

 - one typo in comment is fixed.

Link: http://lkml.kernel.org/r/20170803063822.48702-1-richard.weiyang@gmail.comSigned-off-by: default avatarWei Yang <richard.weiyang@gmail.com>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 88d6ac40
...@@ -2482,7 +2482,7 @@ static unsigned long pvm_determine_end(struct vmap_area **pnext, ...@@ -2482,7 +2482,7 @@ static unsigned long pvm_determine_end(struct vmap_area **pnext,
* matching slot. While scanning, if any of the areas overlaps with * matching slot. While scanning, if any of the areas overlaps with
* existing vmap_area, the base address is pulled down to fit the * existing vmap_area, the base address is pulled down to fit the
* area. Scanning is repeated till all the areas fit and then all * area. Scanning is repeated till all the areas fit and then all
* necessary data structres are inserted and the result is returned. * necessary data structures are inserted and the result is returned.
*/ */
struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets, struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
const size_t *sizes, int nr_vms, const size_t *sizes, int nr_vms,
...@@ -2510,15 +2510,11 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets, ...@@ -2510,15 +2510,11 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
if (start > offsets[last_area]) if (start > offsets[last_area])
last_area = area; last_area = area;
for (area2 = 0; area2 < nr_vms; area2++) { for (area2 = area + 1; area2 < nr_vms; area2++) {
unsigned long start2 = offsets[area2]; unsigned long start2 = offsets[area2];
unsigned long end2 = start2 + sizes[area2]; unsigned long end2 = start2 + sizes[area2];
if (area2 == area) BUG_ON(start2 < end && start < end2);
continue;
BUG_ON(start2 >= start && start2 < end);
BUG_ON(end2 <= end && end2 > start);
} }
} }
last_end = offsets[last_area] + sizes[last_area]; last_end = offsets[last_area] + sizes[last_area];
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment