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.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index a47e389..fa409c9 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2482,7 +2482,7 @@
* matching slot. While scanning, if any of the areas overlaps with
* existing vmap_area, the base address is pulled down to fit the
* 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,
const size_t *sizes, int nr_vms,
@@ -2510,15 +2510,11 @@
if (start > offsets[last_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 end2 = start2 + sizes[area2];
- if (area2 == area)
- continue;
-
- BUG_ON(start2 >= start && start2 < end);
- BUG_ON(end2 <= end && end2 > start);
+ BUG_ON(start2 < end && start < end2);
}
}
last_end = offsets[last_area] + sizes[last_area];