staging: erofs: kill CONFIG_EROFS_FS_USE_VM_MAP_RAM

Turn into a module parameter ("use_vmap") as it
can be set at runtime.
Suggested-by: David Sterba <dsterba@suse.cz>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Link: https://lore.kernel.org/r/20190731155752.210602-15-gaoxiang25@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/erofs/Documentation/filesystems/erofs.txt

@@ -66,6 +66,10 @@ fault_injection=%d     Enable fault injection in all supported types with
 (no)acl                Setup POSIX Access Control List. Note: acl is enabled
                        by default if CONFIG_EROFS_FS_POSIX_ACL is selected.
 
+Module parameters
+=================
+use_vmap=[0|1]         Use vmap() instead of vm_map_ram() (default 0).
+
 On-disk details
 ===============
 

drivers/staging/erofs/Kconfig

@@ -63,14 +63,6 @@ config EROFS_FS_SECURITY
 
 	  If you are not using a security module, say N.
 
-config EROFS_FS_USE_VM_MAP_RAM
-	bool "EROFS VM_MAP_RAM Support"
-	depends on EROFS_FS
-	help
-	  use vm_map_ram/vm_unmap_ram instead of vmap/vunmap.
-
-	  If you don't know what these are, say N.
-
 config EROFS_FAULT_INJECTION
 	bool "EROFS fault injection facility"
 	depends on EROFS_FS

drivers/staging/erofs/decompressor.c

@@ -7,6 +7,7 @@
  * Created by Gao Xiang <gaoxiang25@huawei.com>
  */
 #include "compress.h"
+#include <linux/module.h>
 #include <linux/lz4.h>
 
 #ifndef LZ4_DISTANCE_MAX	/* history window size */
@@ -29,6 +30,10 @@ struct z_erofs_decompressor {
 	char *name;
 };
 
+static bool use_vmap;
+module_param(use_vmap, bool, 0444);
+MODULE_PARM_DESC(use_vmap, "Use vmap() instead of vm_map_ram() (default 0)");
+
 static int lz4_prepare_destpages(struct z_erofs_decompress_req *rq,
 				 struct list_head *pagepool)
 {
@@ -219,29 +224,28 @@ static void copy_from_pcpubuf(struct page **out, const char *dst,
 
 static void *erofs_vmap(struct page **pages, unsigned int count)
 {
-#ifdef CONFIG_EROFS_FS_USE_VM_MAP_RAM
 	int i = 0;
 
+	if (use_vmap)
+		return vmap(pages, count, VM_MAP, PAGE_KERNEL);
+
 	while (1) {
 		void *addr = vm_map_ram(pages, count, -1, PAGE_KERNEL);
+
 		/* retry two more times (totally 3 times) */
 		if (addr || ++i >= 3)
 			return addr;
 		vm_unmap_aliases();
 	}
 	return NULL;
-#else
-	return vmap(pages, count, VM_MAP, PAGE_KERNEL);
-#endif
 }
 
 static void erofs_vunmap(const void *mem, unsigned int count)
 {
-#ifdef CONFIG_EROFS_FS_USE_VM_MAP_RAM
-	vm_unmap_ram(mem, count);
-#else
-	vunmap(mem);
-#endif
+	if (!use_vmap)
+		vm_unmap_ram(mem, count);
+	else
+		vunmap(mem);
 }
 
 static int decompress_generic(struct z_erofs_decompress_req *rq,