linux-kernel - Re: [PATCH] mm, slab: rename kmalloc-node cache to kmalloc-<size>

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Date:   Wed, 8 Feb 2017 10:26:13 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        kbuild test robot <lkp@...el.com>
Cc:     kbuild-all@...org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Joonsoo Kim <iamjoonsoo.kim@....com>,
        David Rientjes <rientjes@...gle.com>,
        Pekka Enberg <penberg@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH] mm, slab: rename kmalloc-node cache to kmalloc-<size>

Sorry, used old Willy's address.

On 02/08/2017 10:12 AM, Vlastimil Babka wrote:
> On 02/07/2017 10:38 PM, Andrew Morton wrote:
>> On Wed, 8 Feb 2017 01:15:17 +0800 kbuild test robot <lkp@...el.com> wrote:
>>
>>> Hi Vlastimil,
>>>
>>> [auto build test WARNING on mmotm/master]
>>> [also build test WARNING on v4.10-rc7 next-20170207]
>>> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
>>>
>>> url:    https://github.com/0day-ci/linux/commits/Vlastimil-Babka/mm-slab-rename-kmalloc-node-cache-to-kmalloc-size/20170204-021843
>>> base:   git://git.cmpxchg.org/linux-mmotm.git master
>>> config: arm-allyesconfig (attached as .config)
>>> compiler: arm-linux-gnueabi-gcc (Debian 6.1.1-9) 6.1.1 20160705
>>> reproduce:
>>>         wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
>>>         chmod +x ~/bin/make.cross
>>>         # save the attached .config to linux build tree
>>>         make.cross ARCH=arm
>>>
>>> All warnings (new ones prefixed by >>):
>>>
>>> >> WARNING: mm/built-in.o(.text+0x3b49c): Section mismatch in reference from the function get_kmalloc_cache_name() to the (unknown reference) .init.rodata:(unknown)
>>>    The function get_kmalloc_cache_name() references
>>>    the (unknown reference) __initconst (unknown).
>>>    This is often because get_kmalloc_cache_name lacks a __initconst
>>>    annotation or the annotation of (unknown) is wrong.
>>
>> yup, thanks.
>
> Thanks for the fix.
>
> I was going to implement Christoph's suggestion and export the whole structure
> in mm/slab.h, but gcc was complaining that I'm redefining it, until I created a
> typedef first. Is it worth the trouble? Below is how it would look like.
>
> Vlastimil
>
> ----8<----
> diff --git a/mm/slab.c b/mm/slab.c
> index ede31b59bb9f..9d66b3d6791e 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1294,7 +1294,7 @@ void __init kmem_cache_init(void)
>  	 * structures first.  Without this, further allocations will bug.
>  	 */
>  	kmalloc_caches[INDEX_NODE] = create_kmalloc_cache(
> -				get_kmalloc_cache_name(INDEX_NODE),
> +				kmalloc_info[INDEX_NODE].name,
>  				kmalloc_size(INDEX_NODE), ARCH_KMALLOC_FLAGS);
>  	slab_state = PARTIAL_NODE;
>  	setup_kmalloc_cache_index_table();
> diff --git a/mm/slab.h b/mm/slab.h
> index 5708c548c6f7..e6b4cf74be86 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -71,6 +71,13 @@ extern struct list_head slab_caches;
>  /* The slab cache that manages slab cache information */
>  extern struct kmem_cache *kmem_cache;
>
> +/* A table of kmalloc cache names and sizes */
> +typedef struct {
> +	const char *name;
> +	unsigned long size;
> +} kmalloc_info_t;
> +extern const kmalloc_info_t kmalloc_info[];
> +
>  unsigned long calculate_alignment(unsigned long flags,
>  		unsigned long align, unsigned long size);
>
> @@ -78,7 +85,6 @@ unsigned long calculate_alignment(unsigned long flags,
>  /* Kmalloc array related functions */
>  void setup_kmalloc_cache_index_table(void);
>  void create_kmalloc_caches(unsigned long);
> -const char *get_kmalloc_cache_name(int index);
>
>  /* Find the kmalloc slab corresponding for a certain size */
>  struct kmem_cache *kmalloc_slab(size_t, gfp_t);
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 36a8547de699..ab3872ed623e 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -917,10 +917,7 @@ struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags)
>   * kmalloc_index() supports up to 2^26=64MB, so the final entry of the table is
>   * kmalloc-67108864.
>   */
> -static struct {
> -	const char *name;
> -	unsigned long size;
> -} const kmalloc_info[] __initconst = {
> +const kmalloc_info_t kmalloc_info[] __initconst = {
>  	{NULL,                      0},		{"kmalloc-96",             96},
>  	{"kmalloc-192",           192},		{"kmalloc-8",               8},
>  	{"kmalloc-16",             16},		{"kmalloc-32",             32},
> @@ -937,11 +934,6 @@ static struct {
>  	{"kmalloc-67108864", 67108864}
>  };
>
> -const char *get_kmalloc_cache_name(int index)
> -{
> -	return kmalloc_info[index].name;
> -}
> -
>  /*
>   * Patch up the size_index table if we have strange large alignment
>   * requirements for the kmalloc array. This is only the case for
>