[PATCH] grab swap token reordered

Make 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 <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: Ashwin Chaugule

mm/filemap.c

@@ -1445,7 +1445,6 @@ struct page *filemap_nopage(struct vm_area_struct *area,
 	 * effect.
 	 */
 	error = page_cache_read(file, pgoff);
-	grab_swap_token();
 
 	/*
 	 * The page we want has now been added to the page cache.

mm/memory.c

@@ -1991,6 +1991,7 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	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) {
@@ -2008,7 +2009,6 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
 		/* 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);