There are four types of kmalloc_caches: KMALLOC_NORMAL, KMALLOC_CGROUP,
KMALLOC_RECLAIM, and KMALLOC_DMA. While the first three types are
created using new_kmalloc_cache(), KMALLOC_DMA caches are created in a
separate logic. Let KMALLOC_DMA caches be also created using
new_kmalloc_cache(), to enhance readability.

Historically, there were only KMALLOC_NORMAL caches and KMALLOC_DMA
caches in the first place, and they were initialized in two separate
logics. However, when KMALLOC_RECLAIM was introduced in v4.20 via
commit 1291523f2c1d ("mm, slab/slub: introduce kmalloc-reclaimable
caches") and KMALLOC_CGROUP was introduced in v5.14 via
commit 494c1dfe855e ("mm: memcg/slab: create a new set of kmalloc-cg-<n>
caches"), their creations were merged with KMALLOC_NORMAL's only.
KMALLOC_DMA creation logic should be merged with them, too.

By merging KMALLOC_DMA initialization with other types, the following
two changes might occur:
1. The order dma-kmalloc-<n> caches added in slab_cache list may be
sorted by size. i.e. the order they appear in /proc/slabinfo may change
as well.
2. slab_state will be set to UP after KMALLOC_DMA is created.
In case of slub, freelist randomization is dependent on slab_state>=UP,
and therefore KMALLOC_DMA cache's freelist will not be randomized in
creation, but will be deferred to init_freelist_randomization().

Co-developed-by: JaeSang Yoo <jsyoo5b@gmail.com>
Signed-off-by: JaeSang Yoo <jsyoo5b@gmail.com>
Signed-off-by: Ohhoon Kwon <ohkwon1043@gmail.com>
---
 mm/slab_common.c | 18 +++---------------
 1 file changed, 3 insertions(+), 15 deletions(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 6ee64d6208b3..a959d247c27b 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -849,6 +849,8 @@ new_kmalloc_cache(int idx, enum kmalloc_cache_type type, slab_flags_t flags)
 			return;
 		}
 		flags |= SLAB_ACCOUNT;
+	} else if (IS_ENABLED(CONFIG_ZONE_DMA) && (type == KMALLOC_DMA)) {
+		flags |= SLAB_CACHE_DMA;
 	}
 
 	kmalloc_caches[type][idx] = create_kmalloc_cache(
@@ -877,7 +879,7 @@ void __init create_kmalloc_caches(slab_flags_t flags)
 	/*
 	 * Including KMALLOC_CGROUP if CONFIG_MEMCG_KMEM defined
 	 */
-	for (type = KMALLOC_NORMAL; type <= KMALLOC_RECLAIM; type++) {
+	for (type = KMALLOC_NORMAL; type < NR_KMALLOC_TYPES; type++) {
 		for (i = KMALLOC_SHIFT_LOW; i <= KMALLOC_SHIFT_HIGH; i++) {
 			if (!kmalloc_caches[type][i])
 				new_kmalloc_cache(i, type, flags);
@@ -898,20 +900,6 @@ void __init create_kmalloc_caches(slab_flags_t flags)
 
 	/* Kmalloc array is now usable */
 	slab_state = UP;
-
-#ifdef CONFIG_ZONE_DMA
-	for (i = 0; i <= KMALLOC_SHIFT_HIGH; i++) {
-		struct kmem_cache *s = kmalloc_caches[KMALLOC_NORMAL][i];
-
-		if (s) {
-			kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache(
-				kmalloc_info[i].name[KMALLOC_DMA],
-				kmalloc_info[i].size,
-				SLAB_CACHE_DMA | flags, 0,
-				kmalloc_info[i].size);
-		}
-	}
-#endif
 }
 #endif /* !CONFIG_SLOB */
 
-- 
2.25.1

On Mon, 11 Apr 2022, Ohhoon Kwon wrote:

> There are four types of kmalloc_caches: KMALLOC_NORMAL, KMALLOC_CGROUP,
> KMALLOC_RECLAIM, and KMALLOC_DMA. While the first three types are
> created using new_kmalloc_cache(), KMALLOC_DMA caches are created in a
> separate logic. Let KMALLOC_DMA caches be also created using
> new_kmalloc_cache(), to enhance readability.
> 
> Historically, there were only KMALLOC_NORMAL caches and KMALLOC_DMA
> caches in the first place, and they were initialized in two separate
> logics. However, when KMALLOC_RECLAIM was introduced in v4.20 via
> commit 1291523f2c1d ("mm, slab/slub: introduce kmalloc-reclaimable
> caches") and KMALLOC_CGROUP was introduced in v5.14 via
> commit 494c1dfe855e ("mm: memcg/slab: create a new set of kmalloc-cg-<n>
> caches"), their creations were merged with KMALLOC_NORMAL's only.
> KMALLOC_DMA creation logic should be merged with them, too.
> 
> By merging KMALLOC_DMA initialization with other types, the following
> two changes might occur:
> 1. The order dma-kmalloc-<n> caches added in slab_cache list may be
> sorted by size. i.e. the order they appear in /proc/slabinfo may change
> as well.
> 2. slab_state will be set to UP after KMALLOC_DMA is created.
> In case of slub, freelist randomization is dependent on slab_state>=UP,
> and therefore KMALLOC_DMA cache's freelist will not be randomized in
> creation, but will be deferred to init_freelist_randomization().
> 
> Co-developed-by: JaeSang Yoo <jsyoo5b@gmail.com>
> Signed-off-by: JaeSang Yoo <jsyoo5b@gmail.com>
> Signed-off-by: Ohhoon Kwon <ohkwon1043@gmail.com>

Acked-by: David Rientjes <rientjes@google.com>