[RFC][PATCH 1/2] grab swap token reordered

[Ashwin Chaugule <ashwin.chaugule@celunite.com>]

This patch makes sure the contention for the token happens _before_ any
read-in and kicks the swap-token algo only when the VM is under
pressure.



Signed-off-by: Ashwin Chaugule <ashwin.chaugule@celunite.com>

--
diff --git a/mm/filemap.c b/mm/filemap.c
index afcdc72..c17b2ab 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1479,7 +1479,6 @@ no_cached_page:
 	 * effect.
 	 */
 	error = page_cache_read(file, pgoff);
-	grab_swap_token();
 
 	/*
 	 * The page we want has now been added to the page cache.
diff --git a/mm/memory.c b/mm/memory.c
index 92a3ebd..4a877e9 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1974,6 +1974,7 @@ static int do_swap_page(struct mm_struct
 	delayacct_set_flag(DELAYACCT_PF_SWAPIN);
 	page = lookup_swap_cache(entry);
 	if (!page) {
+		grab_swap_token(); /* Contend for token _before_ read-in */
  		swapin_readahead(entry, address, vma);
  		page = read_swap_cache_async(entry, vma, address);
 		if (!page) {
@@ -1991,7 +1992,6 @@ static int do_swap_page(struct mm_struct
 		/* Had to read the page from swap area: Major fault */
 		ret = VM_FAULT_MAJOR;
 		count_vm_event(PGMAJFAULT);
-		grab_swap_token();
 	}
 
 	delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
--