linux-kernel - Re: [PATCH v2] mm/slab_common: Support the slub_debug boot option on specific object size

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Date:	Wed, 22 Apr 2015 14:00:39 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Gavin Guo <gavin.guo@...onical.com>
Cc:	cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
	iamjoonsoo.kim@....com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/slab_common: Support the slub_debug boot option
 on specific object size

On Wed, 22 Apr 2015 16:33:38 +0800 Gavin Guo <gavin.guo@...onical.com> wrote:

> The slub_debug=PU,kmalloc-xx cannot work because in the
> create_kmalloc_caches() the s->name is created after the
> create_kmalloc_cache() is called. The name is NULL in the
> create_kmalloc_cache() so the kmem_cache_flags() would not set the
> slub_debug flags to the s->flags. The fix here set up a kmalloc_names
> string array for the initialization purpose and delete the dynamic
> name creation of kmalloc_caches.
> 
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -793,6 +793,26 @@ void __init create_kmalloc_caches(unsigned long flags)
>  	int i;
>  
>  	/*
> +	 * The kmalloc_names is for temporary usage to make
> +	 * slub_debug=,kmalloc-xx option work in the boot time. The
> +	 * kmalloc_index() support to 2^26=64MB. So, the final entry of the
> +	 * table is kmalloc-67108864.
> +	 */
> +	static const char *kmalloc_names[] = {
> +		"0",			"kmalloc-96",		"kmalloc-192",
> +		"kmalloc-8",		"kmalloc-16",		"kmalloc-32",
> +		"kmalloc-64",		"kmalloc-128",		"kmalloc-256",
> +		"kmalloc-512",		"kmalloc-1024",		"kmalloc-2048",
> +		"kmalloc-4196",		"kmalloc-8192",		"kmalloc-16384",
> +		"kmalloc-32768",	"kmalloc-65536",
> +		"kmalloc-131072",	"kmalloc-262144",
> +		"kmalloc-524288",	"kmalloc-1048576",
> +		"kmalloc-2097152",	"kmalloc-4194304",
> +		"kmalloc-8388608",	"kmalloc-16777216",
> +		"kmalloc-33554432",	"kmalloc-67108864"
> +	};
> +
> +	/*
>  	 * Patch up the size_index table if we have strange large alignment
>  	 * requirements for the kmalloc array. This is only the case for
>  	 * MIPS it seems. The standard arches will not generate any code here.
> @@ -835,7 +855,8 @@ void __init create_kmalloc_caches(unsigned long flags)
>  	}
>  	for (i = KMALLOC_SHIFT_LOW; i <= KMALLOC_SHIFT_HIGH; i++) {
>  		if (!kmalloc_caches[i]) {
> -			kmalloc_caches[i] = create_kmalloc_cache(NULL,
> +			kmalloc_caches[i] = create_kmalloc_cache(
> +							kmalloc_names[i],
>  							1 << i, flags);
>  		}

You could do something like

		kmalloc_caches[i] = create_kmalloc_cache(
					kmalloc_names[i],
					kstrtoul(kmalloc_names[i] + 8),
					flags);

here, and remove those weird "96" and "192" cases.

Or if that's considered too messy, make it

	static const struct {
		const char *name;
		unsigned size;
	} kmalloc_cache_info[] = {
		{ NULL, 0 },
		{ "kmalloc-96", 96 },
		...
	};

but I'm thinking the kstrtoul() trick will be OK.

> -	for (i = 0; i <= KMALLOC_SHIFT_HIGH; i++) {
> -		struct kmem_cache *s = kmalloc_caches[i];
> -		char *n;
> -
> -		if (s) {
> -			n = kasprintf(GFP_NOWAIT, "kmalloc-%d", kmalloc_size(i));
> -
> -			BUG_ON(!n);
> -			s->name = n;
> -		}
> -	}
> -

slab_kmem_cache_release() still does kfree_const(s->name).  It will
crash?

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