On Fri, Mar 08, 2019 at 03:14:13PM +1100, Tobin C. Harding wrote:
> Add the two methods needed for moving objects and enable the display of
> the callbacks via the /sys/kernel/slab interface.
>
> Add documentation explaining the use of these methods and the prototypes
> for slab.h. Add functions to setup the callbacks method for a slab
> cache.
>
> Add empty functions for SLAB/SLOB. The API is generic so it could be
> theoretically implemented for these allocators as well.
>
> Co-developed-by: Christoph Lameter <cl@xxxxxxxxx>
> Signed-off-by: Tobin C. Harding <tobin@xxxxxxxxxx>
> ---
> include/linux/slab.h | 69 ++++++++++++++++++++++++++++++++++++++++
> include/linux/slub_def.h | 3 ++
> mm/slab_common.c | 4 +++
> mm/slub.c | 42 ++++++++++++++++++++++++
> 4 files changed, 118 insertions(+)
>
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 11b45f7ae405..22e87c41b8a4 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -152,6 +152,75 @@ void memcg_create_kmem_cache(struct mem_cgroup *, struct kmem_cache *);
> void memcg_deactivate_kmem_caches(struct mem_cgroup *);
> void memcg_destroy_kmem_caches(struct mem_cgroup *);
>
> +/*
> + * Function prototypes passed to kmem_cache_setup_mobility() to enable
> + * mobile objects and targeted reclaim in slab caches.
> + */
> +
> +/**
> + * typedef kmem_cache_isolate_func - Object migration callback function.
> + * @s: The cache we are working on.
> + * @ptr: Pointer to an array of pointers to the objects to migrate.
> + * @nr: Number of objects in array.
> + *
> + * The purpose of kmem_cache_isolate_func() is to pin each object so that
> + * they cannot be freed until kmem_cache_migrate_func() has processed
> + * them. This may be accomplished by increasing the refcount or setting
> + * a flag.
> + *
> + * The object pointer array passed is also passed to
> + * kmem_cache_migrate_func(). The function may remove objects from the
> + * array by setting pointers to NULL. This is useful if we can determine
> + * that an object is being freed because kmem_cache_isolate_func() was
> + * called when the subsystem was calling kmem_cache_free(). In that
> + * case it is not necessary to increase the refcount or specially mark
> + * the object because the release of the slab lock will lead to the
> + * immediate freeing of the object.
> + *
> + * Context: Called with locks held so that the slab objects cannot be
> + * freed. We are in an atomic context and no slab operations
> + * may be performed.
> + * Return: A pointer that is passed to the migrate function. If any
> + * objects cannot be touched at this point then the pointer may
> + * indicate a failure and then the migration function can simply
> + * remove the references that were already obtained. The private
> + * data could be used to track the objects that were already pinned.
> + */
> +typedef void *kmem_cache_isolate_func(struct kmem_cache *s, void **ptr, int nr);
> +
> +/**
> + * typedef kmem_cache_migrate_func - Object migration callback function.
> + * @s: The cache we are working on.
> + * @ptr: Pointer to an array of pointers to the objects to migrate.
> + * @nr: Number of objects in array.
> + * @node: The NUMA node where the object should be allocated.
> + * @private: The pointer returned by kmem_cache_isolate_func().
> + *
> + * This function is responsible for migrating objects. Typically, for
> + * each object in the input array you will want to allocate an new
> + * object, copy the original object, update any pointers, and free the
> + * old object.
> + *
> + * After this function returns all pointers to the old object should now
> + * point to the new object.
> + *
> + * Context: Called with no locks held and interrupts enabled. Sleeping
> + * is possible. Any operation may be performed.
> + */
> +typedef void kmem_cache_migrate_func(struct kmem_cache *s, void **ptr,
> + int nr, int node, void *private);
> +
> +/*
> + * kmem_cache_setup_mobility() is used to setup callbacks for a slab cache.
> + */
> +#ifdef CONFIG_SLUB
> +void kmem_cache_setup_mobility(struct kmem_cache *, kmem_cache_isolate_func,
> + kmem_cache_migrate_func);
> +#else
> +static inline void kmem_cache_setup_mobility(struct kmem_cache *s,
> + kmem_cache_isolate_func isolate, kmem_cache_migrate_func migrate) {}
> +#endif
> +
> /*
> * Please use this macro to create slab caches. Simply specify the
> * name of the structure and maybe some flags that are listed above.
> diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
> index 3a1a1dbc6f49..a7340a1ed5dc 100644
> --- a/include/linux/slub_def.h
> +++ b/include/linux/slub_def.h
> @@ -99,6 +99,9 @@ struct kmem_cache {
> gfp_t allocflags; /* gfp flags to use on each alloc */
> int refcount; /* Refcount for slab cache destroy */
> void (*ctor)(void *);
> + kmem_cache_isolate_func *isolate;
> + kmem_cache_migrate_func *migrate;
> +
> unsigned int inuse; /* Offset to metadata */
> unsigned int align; /* Alignment */
> unsigned int red_left_pad; /* Left redzone padding size */
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index f9d89c1b5977..754acdb292e4 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -298,6 +298,10 @@ int slab_unmergeable(struct kmem_cache *s)
> if (!is_root_cache(s))
> return 1;
>
> + /*
> + * s->isolate and s->migrate imply s->ctor so no need to
> + * check them explicitly.
> + */
> if (s->ctor)
> return 1;
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 69164aa7cbbf..0133168d1089 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -4325,6 +4325,34 @@ int __kmem_cache_create(struct kmem_cache *s, slab_flags_t flags)
> return err;
> }
>
> +void kmem_cache_setup_mobility(struct kmem_cache *s,
> + kmem_cache_isolate_func isolate,
> + kmem_cache_migrate_func migrate)
> +{
I wonder if it's better to adapt kmem_cache_create() to take two additional
argument? I suspect mobility is not a dynamic option, so it can be
set on kmem_cache creation.
> + /*
> + * Mobile objects must have a ctor otherwise the object may be
> + * in an undefined state on allocation. Since the object may
> + * need to be inspected by the migration function at any time
> + * after allocation we must ensure that the object always has a
> + * defined state.
> + */
> + if (!s->ctor) {
> + pr_err("%s: cannot setup mobility without a constructor\n",
> + s->name);
> + return;
> + }
> +
> + s->isolate = isolate;
> + s->migrate = migrate;
> +
> + /*
> + * Sadly serialization requirements currently mean that we have
> + * to disable fast cmpxchg based processing.
> + */
Can you, please, elaborate a bit more here?
> + s->flags &= ~__CMPXCHG_DOUBLE;
> +}
> +EXPORT_SYMBOL(kmem_cache_setup_mobility);
> +
> void *__kmalloc_track_caller(size_t size, gfp_t gfpflags, unsigned long caller)
> {
> struct kmem_cache *s;
> @@ -5018,6 +5046,20 @@ static ssize_t ops_show(struct kmem_cache *s, char *buf)
>
> if (s->ctor)
> x += sprintf(buf + x, "ctor : %pS\n", s->ctor);
> +
> + if (s->isolate) {
> + x += sprintf(buf + x, "isolate : ");
> + x += sprint_symbol(buf + x,
> + (unsigned long)s->isolate);
> + x += sprintf(buf + x, "\n");
> + }
Is there a reason why s->ctor and s->isolate/migrate are printed
using different methods?
> +
> + if (s->migrate) {
> + x += sprintf(buf + x, "migrate : ");
> + x += sprint_symbol(buf + x,
> + (unsigned long)s->migrate);
> + x += sprintf(buf + x, "\n");
> + }
> return x;
> }
> SLAB_ATTR_RO(ops);
> --
> 2.21.0
>
Thanks!
