mm: swap: remove unneeded cgroup_throttle_swaprate()

All the callers of cgroup_throttle_swaprate() are converted to
folio_throttle_swaprate(), so make __cgroup_throttle_swaprate() to take a
folio, and rename it to __folio_throttle_swaprate(), also rename gfp_mask
to gfp and drop redundant extern keyword.  finally, drop unused
cgroup_throttle_swaprate().

Link: https://lkml.kernel.org/r/20230302115835.105364-8-wangkefeng.wang@huawei.com
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/swap.h

@@ -641,22 +641,18 @@ extern atomic_t zswap_stored_pages;
 #endif
 
 #if defined(CONFIG_SWAP) && defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
-extern void __cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask);
-static inline  void cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask)
+void __folio_throttle_swaprate(struct folio *folio, gfp_t gfp);
+static inline void folio_throttle_swaprate(struct folio *folio, gfp_t gfp)
 {
 	if (mem_cgroup_disabled())
 		return;
-	__cgroup_throttle_swaprate(page, gfp_mask);
+	__folio_throttle_swaprate(folio, gfp);
 }
 #else
-static inline void cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask)
+static inline void folio_throttle_swaprate(struct folio *folio, gfp_t gfp)
 {
 }
 #endif
-static inline void folio_throttle_swaprate(struct folio *folio, gfp_t gfp)
-{
-	cgroup_throttle_swaprate(&folio->page, gfp);
-}
 
 #if defined(CONFIG_MEMCG) && defined(CONFIG_SWAP)
 void mem_cgroup_swapout(struct folio *folio, swp_entry_t entry);

mm/swapfile.c

@@ -3635,12 +3635,12 @@ static void free_swap_count_continuations(struct swap_info_struct *si)
 }
 
 #if defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
-void __cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask)
+void __folio_throttle_swaprate(struct folio *folio, gfp_t gfp)
 {
 	struct swap_info_struct *si, *next;
-	int nid = page_to_nid(page);
+	int nid = folio_nid(folio);
 
-	if (!(gfp_mask & __GFP_IO))
+	if (!(gfp & __GFP_IO))
 		return;
 
 	if (!blk_cgroup_congested())