diff mbox series

[2/2] mm: slab: fix comment for __assume_kmalloc_alignment

Message ID 84d8142747230f2015eaf9705ee7c2e1a9f56596.1651161548.git.andreyknvl@google.com (mailing list archive)
State New
Headers show
Series [1/2] mm: slab: fix comment for ARCH_KMALLOC_MINALIGN | expand

Commit Message

andrey.konovalov@linux.dev April 28, 2022, 3:59 p.m. UTC 
From: Andrey Konovalov <andreyknvl@google.com>

The comment next to the __assume_kmalloc_alignment definition is not
precise: kmalloc relies on kmem_cache_alloc, so kmalloc technically returns
pointers aligned to both ARCH_KMALLOC_MINALIGN and ARCH_SLAB_MINALIGN,
not only to ARCH_KMALLOC_MINALIGN.

(See create_kmalloc_cache()->create_boot_cache()->calculate_alignment()
 for SLAB and SLUB and __do_kmalloc_node() for SLOB.)

Clarify the comment.

The assumption specified by __assume_kmalloc_alignment is still correct,
although it can be made stronger. I'll leave this to a separate patch.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 include/linux/slab.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Comments

David Rientjes May 2, 2022, 12:13 a.m. UTC | #1 
On Thu, 28 Apr 2022, andrey.konovalov@linux.dev wrote:

> From: Andrey Konovalov <andreyknvl@google.com>
> 
> The comment next to the __assume_kmalloc_alignment definition is not
> precise: kmalloc relies on kmem_cache_alloc, so kmalloc technically returns
> pointers aligned to both ARCH_KMALLOC_MINALIGN and ARCH_SLAB_MINALIGN,
> not only to ARCH_KMALLOC_MINALIGN.
> 
> (See create_kmalloc_cache()->create_boot_cache()->calculate_alignment()
>  for SLAB and SLUB and __do_kmalloc_node() for SLOB.)
> 
> Clarify the comment.
> 
> The assumption specified by __assume_kmalloc_alignment is still correct,
> although it can be made stronger. I'll leave this to a separate patch.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

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

Patch

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 8cc1d54e56ad..06323a4beff0 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -210,9 +210,9 @@  void kmem_dump_obj(void *object);
 #endif
 
 /*
- * kmalloc and friends return ARCH_KMALLOC_MINALIGN aligned
- * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MINALIGN
- * aligned pointers.
+ * kmem_cache_alloc and friends return pointers aligned to ARCH_SLAB_MINALIGN.
+ * kmalloc and friends return pointers aligned to both ARCH_KMALLOC_MINALIGN
+ * and ARCH_SLAB_MINALIGN, but here we only assume the former alignment.
  */
 #define __assume_kmalloc_alignment __assume_aligned(ARCH_KMALLOC_MINALIGN)
 #define __assume_slab_alignment __assume_aligned(ARCH_SLAB_MINALIGN)