On Mon, Mar 11, 2019 at 09:51:09PM +0000, Roman Gushchin wrote:
> 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.
Thanks for the review. You are correct mobility is not dynamic (at the
moment once enabled it cannot be disabled). I don't think we want to
change every caller of kmem_cache_create() though, adding two new
parameters that are almost always going to be NULL. Also, I cannot ATM
see how object migration would be useful to SLOB so changing the API for
all slab allocators does not seem like a good thing.
thanks,
Tobin.
