On 9/24/18 2:46 AM, Andrey Ryabinin wrote:
On 09/24/2018 01:42 AM, Ming Lei wrote:
On Fri, Sep 21, 2018 at 03:04:18PM +0200, Vitaly Kuznetsov wrote:
Christoph Hellwig <hch@xxxxxx> writes:
On Wed, Sep 19, 2018 at 05:15:43PM +0800, Ming Lei wrote:
1) does kmalloc-N slab guarantee to return N-byte aligned buffer? If
yes, is it a stable rule?
This is the assumption in a lot of the kernel, so I think if somethings
breaks this we are in a lot of pain.
This assumption is not correct. And it's not correct at least from the beginning of the
git era, which is even before SLUB allocator appeared. With CONFIG_DEBUG_SLAB=y
the same as with CONFIG_SLUB_DEBUG_ON=y kmalloc return 'unaligned' objects.
The guaranteed arch-and-config-independent alignment of kmalloc() result is "sizeof(void*)".
If objects has higher alignment requirement, the could be allocated via specifically created kmem_cache.
Hello Andrey,
The above confuses me. Can you explain to me why the following comment
is present in include/linux/slab.h?
/*
* kmalloc and friends return ARCH_KMALLOC_MINALIGN aligned
* pointers. kmem_cache_alloc and friends return ARCH_SLAB_MINALIGN
* aligned pointers.
*/
Thanks,
Bart.
