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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>
This commit is contained in:
Wei Yang 2017-09-06 16:24:09 -07:00 committed by Linus Torvalds
parent 88d6ac40c1
commit c568da282b
1 changed files with 3 additions and 7 deletions
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10
mm/vmalloc.c
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@ -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];