mm, slab: Make kmalloc_info[] contain all types of names

Changes in v3
--
1. restore __initconst (patch 1/4)
2. rename patch 3/4
3. add more clarification for patch 4/4

Changes in v2
--
1. remove __initconst (patch 1/5)
2. squash patch 2/5
3. add ack tag from Vlastimil Babka

There are three types of kmalloc, KMALLOC_NORMAL, KMALLOC_RECLAIM and KMALLOC_DMA.

The name of KMALLOC_NORMAL is contained in kmalloc_info[].name, but the names of KMALLOC_RECLAIM and KMALLOC_DMA are dynamically generated by kmalloc_cache_name().

Patch1 predefines the names of all types of kmalloc to save the time spent dynamically generating names.

The other 4 patches did some cleanup work.

These changes make sense, and the time spent by new_kmalloc_cache() has been reduced by approximately 36.3%.

Time spent by
new_kmalloc_cache()
5.3-rc7 66264
5.3-rc7+patch 42188

Pengfei Li (4):
mm, slab: Make kmalloc_info[] contain all types of names mm, slab: Remove unused kmalloc_size()
mm, slab_common: use enum kmalloc_cache_type to iterate over kmalloc
caches
mm, slab_common: Make the loop for initializing KMALLOC_DMA start from

    1

 include/linux/slab.h |  20 ---------
 mm/slab.c            |   7 +--
 mm/slab.h            |   2 +-
 mm/slab_common.c     | 101 +++++++++++++++++++++++--------------------
 4 files changed, 59 insertions(+), 71 deletions(-)

2.21.0

There are three types of kmalloc, KMALLOC_NORMAL, KMALLOC_RECLAIM and KMALLOC_DMA.

The name of KMALLOC_NORMAL is contained in kmalloc_info[].name, but the names of KMALLOC_RECLAIM and KMALLOC_DMA are dynamically generated by kmalloc_cache_name().

This patch predefines the names of all types of kmalloc to save the time spent dynamically generating names.

Besides, remove the kmalloc_cache_name() that is no longer used.

---
 mm/slab.c        |  2 +-
 mm/slab.h        |  2 +-
 mm/slab_common.c | 91 ++++++++++++++++++++++++++----------------------
 3 files changed, 51 insertions(+), 44 deletions(-)

index 9df370558e5d..c42b6211f42e 100644
@@ -1247,7 +1247,7 @@ void __init kmem_cache_init(void)
 	 * structures first.  Without this, further allocations will bug.
 	 */
 	kmalloc_caches[KMALLOC_NORMAL][INDEX_NODE] = create_kmalloc_cache(
-				kmalloc_info[INDEX_NODE].name,
+				kmalloc_info[INDEX_NODE].name[KMALLOC_NORMAL],
 				kmalloc_size(INDEX_NODE), ARCH_KMALLOC_FLAGS,
 				0, kmalloc_size(INDEX_NODE));
 	slab_state = PARTIAL_NODE;

index 9057b8056b07..2fc8f956906a 100644
@@ -76,7 +76,7 @@ extern struct kmem_cache *kmem_cache;
 
 /* A table of kmalloc cache names and sizes */
 extern const struct kmalloc_info_struct {
-	const char *name;
+	const char *name[NR_KMALLOC_TYPES];
 	unsigned int size;
 } kmalloc_info[];
 

2.21.0

The size of kmalloc can be obtained from kmalloc_info[], so remove kmalloc_size() that will not be used anymore.

---
 include/linux/slab.h | 20 --------------------
 mm/slab.c            |  5 +++--
 mm/slab_common.c     |  5 ++---
 3 files changed, 5 insertions(+), 25 deletions(-)

index 56c9c7eed34e..e773e5764b7b 100644
@@ -557,26 +557,6 @@ static __always_inline void *kmalloc(size_t size, gfp_t flags)
 	return __kmalloc(size, flags);
 }
 
-/*
- * Determine size used for the nth kmalloc cache.
- * return size or 0 if a kmalloc cache for that
- * size does not exist
- */
-static __always_inline unsigned int kmalloc_size(unsigned int n)
-{
-#ifndef CONFIG_SLOB
-	if (n > 2)
-		return 1U << n;
-
-	if (n == 1 && KMALLOC_MIN_SIZE <= 32)
-		return 96;
-
-	if (n == 2 && KMALLOC_MIN_SIZE <= 64)
-		return 192;
-#endif
-	return 0;
-}
-
 static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node)
 {
 #ifndef CONFIG_SLOB

index c42b6211f42e..7bc4e90e1147 100644
@@ -1248,8 +1248,9 @@ void __init kmem_cache_init(void)
 	 */
 	kmalloc_caches[KMALLOC_NORMAL][INDEX_NODE] = create_kmalloc_cache(
 				kmalloc_info[INDEX_NODE].name[KMALLOC_NORMAL],
-				kmalloc_size(INDEX_NODE), ARCH_KMALLOC_FLAGS,
-				0, kmalloc_size(INDEX_NODE));
+				kmalloc_info[INDEX_NODE].size,
+				ARCH_KMALLOC_FLAGS, 0,
+				kmalloc_info[INDEX_NODE].size);
 	slab_state = PARTIAL_NODE;
 	setup_kmalloc_cache_index_table();
 

index 002e16673581..8b542cfcc4f2 100644
@@ -1239,11 +1239,10 @@ void __init create_kmalloc_caches(slab_flags_t flags)
 		struct kmem_cache *s = kmalloc_caches[KMALLOC_NORMAL][i];
 
 		if (s) {
-			unsigned int size = kmalloc_size(i);
-
 			kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache(
 				kmalloc_info[i].name[KMALLOC_DMA],
-				size, SLAB_CACHE_DMA | flags, 0, 0);
+				kmalloc_info[i].size,
+				SLAB_CACHE_DMA | flags, 0, 0);
 		}
 	}
 #endif

2.21.0

The type of local variable *type* of new_kmalloc_cache() should be enum kmalloc_cache_type instead of int, so correct it.

---
 mm/slab_common.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

index 8b542cfcc4f2..af45b5278fdc 100644
@@ -1192,7 +1192,7 @@ void __init setup_kmalloc_cache_index_table(void)
 }
 
 static void __init
-new_kmalloc_cache(int idx, int type, slab_flags_t flags)
+new_kmalloc_cache(int idx, enum kmalloc_cache_type type, slab_flags_t flags)
 {
 	if (type == KMALLOC_RECLAIM)
 		flags |= SLAB_RECLAIM_ACCOUNT;

@@ -1210,7 +1210,8 @@ new_kmalloc_cache(int idx, int type, slab_flags_t flags)
  */
 void __init create_kmalloc_caches(slab_flags_t flags)
 {
-	int i, type;
+	int i;
+	enum kmalloc_cache_type type;
 
 	for (type = KMALLOC_NORMAL; type <= KMALLOC_RECLAIM; type++) {
 		for (i = KMALLOC_SHIFT_LOW; i <= KMALLOC_SHIFT_HIGH; i++) {

2.21.0

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.

---
 mm/slab_common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index af45b5278fdc..c81fc7dc2946 100644
@@ -1236,7 +1236,7 @@ void __init create_kmalloc_caches(slab_flags_t flags)
 	slab_state = UP;
 
 #ifdef CONFIG_ZONE_DMA
-	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) {

2.21.0

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.)

Yes, I agree with you.
This really makes the code more subtle.

In the past two days, I am working on what you suggested.

So far, I have completed the coding work, but I need some time to make sure there are no bugs and verify the impact on performance.

I will send v4 soon.

Thank you for your review and suggestions.

--
Pengfei

Great!

It would probably be hard to measure with sufficient confidence in terms of runtime performance, but you could use e.g. ./scripts/bloat-o-meter to look for unexpected code increase due to compile-time optimizations becoming runtime.