Retire kmem_virt()

The initial port of ZFS to Linux required a way to identify virtual
memory to make IO to virtual memory backed slabs work, so kmem_virt()
was created. Linux 2.6.25 introduced is_vmalloc_addr(), which is
logically equivalent to kmem_virt(). Support for kernels before 2.6.26
was later dropped and more recently, support for kernels before Linux
2.6.32 has been dropped. We retire kmem_virt() in favor of
is_vmalloc_addr() to cleanup the code.

Signed-off-by: Richard Yao <ryao@gentoo.org>

include/sys/kmem.h

@@ -402,8 +402,6 @@ void spl_kmem_fini(void);
 #define kmem_cache_reap_now(skc)	\
         spl_kmem_cache_reap_now(skc, skc->skc_reap)
 #define kmem_reap()			spl_kmem_reap()
-#define kmem_virt(ptr)			(((ptr) >= (void *)VMALLOC_START) && \
-					 ((ptr) <  (void *)VMALLOC_END))
 
 /*
  * Allow custom slab allocation flags to be set for KMC_SLAB based caches.

module/spl/spl-kmem.c

@@ -1976,7 +1976,7 @@ spl_kmem_cache_free(spl_kmem_cache_t *skc, void *obj)
 	 * are guaranteed to have physical addresses.  They must be removed
 	 * from the tree of emergency objects and the freed.
 	 */
-	if ((skc->skc_flags & KMC_VMEM) && !kmem_virt(obj))
+	if ((skc->skc_flags & KMC_VMEM) && !is_vmalloc_addr(obj))
 		SGOTO(out, spl_emergency_free(skc, obj));
 
 	local_irq_save(flags);