[PATCH 14/17] mm/percpu: micro-optimize pcpu_is_populated()

Yury Norov
2021-08-14T21:20:10Z

bitmap_next_clear_region() calls find_next_zero_bit() and find_next_bit()
sequentially to find a range of clear bits. In case of pcpu_is_populated()
there's a chance to return earlier if bitmap has all bits set.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Dennis Zhou <dennis@kernel.org>
---
mm/percpu.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index a43039629aa4..8bf8b88446d7 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1070,17 +1070,18 @@ static void pcpu_block_update_hint_free(struct pcpu_chunk *chunk, int bit_off,
static bool pcpu_is_populated(struct pcpu_chunk *chunk, int bit_off, int bits,
int *next_off)
{
- unsigned int page_start, page_end, rs, re;
+ unsigned int start, end;

- page_start = PFN_DOWN(bit_off * PCPU_MIN_ALLOC_SIZE);
- page_end = PFN_UP((bit_off + bits) * PCPU_MIN_ALLOC_SIZE);
+ start = PFN_DOWN(bit_off * PCPU_MIN_ALLOC_SIZE);
+ end = PFN_UP((bit_off + bits) * PCPU_MIN_ALLOC_SIZE);

- rs = page_start;
- bitmap_next_clear_region(chunk->populated, &rs, &re, page_end);
- if (rs >= page_end)
+ start = find_next_zero_bit(chunk->populated, end, start);
+ if (start >= end)
return true;

- *next_off = re * PAGE_SIZE / PCPU_MIN_ALLOC_SIZE;
+ end = find_next_bit(chunk->populated, end, start + 1);
+
+ *next_off = end * PAGE_SIZE / PCPU_MIN_ALLOC_SIZE;
return false;
}

--
2.30.2