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SubjectRe: [slubllv6 06/17] slub: Add cmpxchg_double_slab()
On Thu, 26 May 2011, Christoph Lameter wrote:

> Add a function that operates on the second doubleword in the page struct
> and manipulates the object counters, the freelist and the frozen attribute.
>
> Signed-off-by: Christoph Lameter <cl@linux.com>
>
> ---
> include/linux/slub_def.h | 1 +
> mm/slub.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 46 insertions(+)
>
> Index: linux-2.6/mm/slub.c
> ===================================================================
> --- linux-2.6.orig/mm/slub.c 2011-05-16 11:46:33.591463082 -0500
> +++ linux-2.6/mm/slub.c 2011-05-16 11:46:51.181463060 -0500
> @@ -131,6 +131,9 @@ static inline int kmem_cache_debug(struc
> /* Enable to test recovery from slab corruption on boot */
> #undef SLUB_RESILIENCY_TEST
>
> +/* Enable to log cmpxchg failures */
> +#undef SLUB_DEBUG_CMPXCHG
> +
> /*
> * Mininum number of partial slabs. These will be left on the partial
> * lists even if they are empty. kmem_cache_shrink may reclaim them.
> @@ -170,6 +173,7 @@ static inline int kmem_cache_debug(struc
>
> /* Internal SLUB flags */
> #define __OBJECT_POISON 0x80000000UL /* Poison object */
> +#define __CMPXCHG_DOUBLE 0x40000000UL /* Use cmpxchg_double */
>
> static int kmem_size = sizeof(struct kmem_cache);
>
> @@ -354,6 +358,37 @@ static void get_map(struct kmem_cache *s
> set_bit(slab_index(p, s, addr), map);
> }
>
> +static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
> + void *freelist_old, unsigned long counters_old,
> + void *freelist_new, unsigned long counters_new,
> + const char *n)

This is defined only under CONFIG_SLUB_DEBUG, which is surely a mistake:

mm/slub.c: In function ‘acquire_slab’:
mm/slub.c:1460: error: implicit declaration of function ‘cmpxchg_double_slab’

> +{
> +#ifdef CONFIG_CMPXCHG_DOUBLE
> + if (s->flags & __CMPXCHG_DOUBLE) {
> + if (cmpxchg_double(&page->freelist,
> + freelist_old, counters_old,
> + freelist_new, counters_new))
> + return 1;
> + } else
> +#endif
> + {
> + if (page->freelist == freelist_old && page->counters == counters_old) {
> + page->freelist = freelist_new;
> + page->counters = counters_new;
> + return 1;
> + }
> + }
> +
> + cpu_relax();
> + stat(s, CMPXCHG_DOUBLE_FAIL);
> +
> +#ifdef SLUB_DEBUG_CMPXCHG
> + printk(KERN_INFO "%s %s: cmpxchg double redo ", n, s->name);
> +#endif
> +
> + return 0;
> +}
> +
> /*
> * Debug settings:
> */
> @@ -2596,6 +2631,12 @@ static int kmem_cache_open(struct kmem_c
> }
> }
>
> +#ifdef CONFIG_CMPXCHG_DOUBLE
> + if (system_has_cmpxchg_double() && (s->flags & SLAB_DEBUG_FLAGS) == 0)
> + /* Enable fast mode */
> + s->flags |= __CMPXCHG_DOUBLE;
> +#endif
> +

Not sure why this is excluded for SLAB_DEBUG_FLAGS? If it really should
be, then we should clear __CMPXCHG_DOUBLE if debugging features are
enabled through sysfs as well.
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