Re: [PATCH v3 4/4] mm, slab_common: Make the loop for initializing KMALLOC_DMA start from 1

From: Vlastimil Babka
Date: Tue Sep 10 2019 - 06:26:19 EST

On 9/10/19 3:26 AM, Pengfei Li wrote:
KMALLOC_DMA will be initialized only if KMALLOC_NORMAL with
the same index exists.

And kmalloc_caches[KMALLOC_NORMAL][0] is always NULL.

Therefore, the loop that initializes KMALLOC_DMA should start
at 1 instead of 0, which will reduce 1 meaningless attempt.

IMHO the saving of one iteration isn't worth making the code more subtle. KMALLOC_SHIFT_LOW would be nice, but that would skip 1 + 2 which are special.

Since you're doing these cleanups, have you considered reordering kmalloc_info, size_index, kmalloc_index() etc so that sizes 96 and 192 are ordered naturally between 64, 128 and 256? That should remove various special casing such as in create_kmalloc_caches(). I can't guarantee it will be possible without breaking e.g. constant folding optimizations etc., but seems to me it should be feasible. (There are definitely more places to change than those I listed.)

Signed-off-by: Pengfei Li <lpf.vector@xxxxxxxxx>
mm/slab_common.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index af45b5278fdc..c81fc7dc2946 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1236,7 +1236,7 @@ void __init create_kmalloc_caches(slab_flags_t flags)
slab_state = UP;
- for (i = 0; i <= KMALLOC_SHIFT_HIGH; i++) {
+ for (i = 1; i <= KMALLOC_SHIFT_HIGH; i++) {
struct kmem_cache *s = kmalloc_caches[KMALLOC_NORMAL][i];
if (s) {