From: Wonhyuk Yang <vvghjk1234@xxxxxxxxx>
Best upa is determined by iterating 1 to max_upa. If the size of
alloc_size is power of 2, numbers of iteration decrease to
logarithmic level.
Prime factorization of alloc_size makes it easy to get possible
upas. When alloc_size is power of 2, we can avoid cost of the
prime factorization and possible upas are 1, 2, 4, ... max_upa.
Signed-off-by: Wonhyuk Yang <vvghjk1234@xxxxxxxxx>
---
mm/percpu.c | 20 ++++++++------------
1 file changed, 8 insertions(+), 12 deletions(-)
diff --git a/mm/percpu.c b/mm/percpu.c
index 66a93f096394..a24f3973744f 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -2689,18 +2689,17 @@ static struct pcpu_alloc_info * __init pcpu_build_alloc_info(
/*
* Determine min_unit_size, alloc_size and max_upa such that
- * alloc_size is multiple of atom_size and is the smallest
- * which can accommodate 4k aligned segments which are equal to
- * or larger than min_unit_size.
+ * alloc_size is the maximu value of min_unit_size, atom_size.
+ * Also, alloc_size is power of 2 because both min_unit_size
+ * and atom_size are power of 2.
*/
min_unit_size = max_t(size_t, size_sum, PCPU_MIN_UNIT_SIZE);
+ min_unit_size = roundup_pow_of_two(min_unit_size);
/* determine the maximum # of units that can fit in an allocation */
- alloc_size = roundup(min_unit_size, atom_size);
- upa = alloc_size / min_unit_size;
- while (alloc_size % upa || (offset_in_page(alloc_size / upa)))
- upa--;
- max_upa = upa;
+ alloc_size = max_t(size_t, min_unit_size, atom_size);
+ max_upa = alloc_size / min_unit_size;
+
/* group cpus according to their proximity */
for_each_possible_cpu(cpu) {
@@ -2727,12 +2726,9 @@ static struct pcpu_alloc_info * __init pcpu_build_alloc_info(
* Related to atom_size, which could be much larger than the unit_size.
*/
last_allocs = INT_MAX;
- for (upa = max_upa; upa; upa--) {
+ for (upa = max_upa; upa; upa >>= 1) {
int allocs = 0, wasted = 0;
- if (alloc_size % upa || (offset_in_page(alloc_size / upa)))
- continue;
-
for (group = 0; group < nr_groups; group++) {
int this_allocs = DIV_ROUND_UP(group_cnt[group], upa);
allocs += this_allocs;
--
2.17.1
