mm: constify page_is_pfmemalloc() argument

mainline inclusion
from mainline-v5.12-rc1-dontuse
commit 1d7bab6a
category: feature
bugzilla: 173966
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1d7bab6a94458e959f3f55788fd50ddc7d97403b

----------------------------------------------------------------------

The function only tests for page->index, so its argument should be
const.
Signed-off-by: NAlexander Lobakin <alobakin@pm.me>
Reviewed-by: NJesse Brandeburg <jesse.brandeburg@intel.com>
Acked-by: NDavid Rientjes <rientjes@google.com>
Signed-off-by: NJakub Kicinski <kuba@kernel.org>
Reviewed-by: NYongxin Li <liyongxin1@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

include/linux/mm.h

@@ -1596,7 +1596,7 @@ struct address_space *page_mapping_file(struct page *page);
  * ALLOC_NO_WATERMARKS and the low watermark was not
  * met implying that the system is under some pressure.
  */
-static inline bool page_is_pfmemalloc(struct page *page)
+static inline bool page_is_pfmemalloc(const struct page *page)
 {
 	/*
 	 * Page index cannot be this large so this must be