slab: remove struct kmem_cache_cpu

The cpu slab is not used anymore for allocation or freeing, the
remaining code is for flushing, but it's effectively dead.  Remove the
whole struct kmem_cache_cpu, the flushing code and other orphaned
functions.

The remaining used field of kmem_cache_cpu is the stat array with
CONFIG_SLUB_STATS. Put it instead in a new struct kmem_cache_stats.
In struct kmem_cache, the field is cpu_stats and placed near the
end of the struct.

Reviewed-by: Hao Li <hao.li@linux.dev>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Author: tehcaster

mm/slab.h

@@ -21,14 +21,12 @@
 # define system_has_freelist_aba()	system_has_cmpxchg128()
 # define try_cmpxchg_freelist		try_cmpxchg128
 # endif
-#define this_cpu_try_cmpxchg_freelist	this_cpu_try_cmpxchg128
 typedef u128 freelist_full_t;
 #else /* CONFIG_64BIT */
 # ifdef system_has_cmpxchg64
 # define system_has_freelist_aba()	system_has_cmpxchg64()
 # define try_cmpxchg_freelist		try_cmpxchg64
 # endif
-#define this_cpu_try_cmpxchg_freelist	this_cpu_try_cmpxchg64
 typedef u64 freelist_full_t;
 #endif /* CONFIG_64BIT */
 
@@ -189,7 +187,6 @@ struct kmem_cache_order_objects {
  * Slab cache management.
  */
 struct kmem_cache {
-	struct kmem_cache_cpu __percpu *cpu_slab;
 	struct slub_percpu_sheaves __percpu *cpu_sheaves;
 	/* Used for retrieving partial slabs, etc. */
 	slab_flags_t flags;
@@ -238,6 +235,10 @@ struct kmem_cache {
 	unsigned int usersize;		/* Usercopy region size */
 #endif
 
+#ifdef CONFIG_SLUB_STATS
+	struct kmem_cache_stats __percpu *cpu_stats;
+#endif
+
 	struct kmem_cache_node *node[MAX_NUMNODES];
 };