mm/vmalloc.c: halve the number of comparisons performed in pcpu_get_vm_areas() (c568da28) · Commits · 戴 / test

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>

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];

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