zsmalloc: require GFP in zs_malloc()

Pass GFP flags to zs_malloc() instead of using a fixed mask supplied to
zs_create_pool(), so we can be more flexible, but, more importantly, we
need this to switch zram to per-cpu compression streams -- zram will try
to allocate handle with preemption disabled in a fast path and switch to
a slow path (using different gfp mask) if the fast one has failed.

Apart from that, this also align zs_malloc() interface with zspool/zbud.

[sergey.senozhatsky@gmail.com: pass GFP flags to zs_malloc() instead of using a fixed mask]
  Link: http://lkml.kernel.org/r/20160429150942.GA637@swordfish
Link: http://lkml.kernel.org/r/20160429150942.GA637@swordfish
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/zsmalloc.h b/include/linux/zsmalloc.h
index 34eb160..57a8e98 100644
--- a/include/linux/zsmalloc.h
+++ b/include/linux/zsmalloc.h
@@ -41,10 +41,10 @@
 
 struct zs_pool;
 
-struct zs_pool *zs_create_pool(const char *name, gfp_t flags);
+struct zs_pool *zs_create_pool(const char *name);
 void zs_destroy_pool(struct zs_pool *pool);
 
-unsigned long zs_malloc(struct zs_pool *pool, size_t size);
+unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t flags);
 void zs_free(struct zs_pool *pool, unsigned long obj);
 
 void *zs_map_object(struct zs_pool *pool, unsigned long handle,