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

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: 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

mm/vmalloc.c

+3 −7
Original line number Diff line number Diff line
@@ -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

 * 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 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets, 
		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];