[PATCH] empty the deferred lru-addition buffers in swapin_readahead

If we're about to return to userspace after performing some swap
readahead, the pages in the deferred-addition LRU queues could stay
there for some time.  So drain them after performing readahead.

include/linux/pagevec.h

@@ -21,7 +21,6 @@ void __pagevec_release_nonlru(struct pagevec *pvec);
 void __pagevec_free(struct pagevec *pvec);
 void __pagevec_lru_add(struct pagevec *pvec);
 void __pagevec_lru_add_active(struct pagevec *pvec);
-void lru_add_drain(void);
 void pagevec_deactivate_inactive(struct pagevec *pvec);
 void pagevec_strip(struct pagevec *pvec);
 unsigned int pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,

include/linux/swap.h

@@ -158,6 +158,7 @@ extern int FASTCALL(page_over_rsslimit(struct page *));
 extern void FASTCALL(lru_cache_add(struct page *));
 extern void FASTCALL(lru_cache_add_active(struct page *));
 extern void FASTCALL(activate_page(struct page *));
+void lru_add_drain(void);
 
 extern void swap_setup(void);
 

mm/memory.c

@@ -967,12 +967,13 @@ void swapin_readahead(swp_entry_t entry)
 	num = valid_swaphandles(entry, &offset);
 	for (i = 0; i < num; offset++, i++) {
 		/* Ok, do the async read-ahead now */
-		new_page = read_swap_cache_async(swp_entry(swp_type(entry), offset));
+		new_page = read_swap_cache_async(swp_entry(swp_type(entry),
+						offset));
 		if (!new_page)
 			break;
 		page_cache_release(new_page);
 	}
-	return;
+	lru_add_drain();	/* Push any new pages onto the LRU now */
 }
 
 /*
@@ -1007,7 +1008,7 @@ static int do_swap_page(struct mm_struct * mm,
 				ret = VM_FAULT_MINOR;
 			pte_unmap(page_table);
 			spin_unlock(&mm->page_table_lock);
-			return ret;
+			goto out;
 		}
 
 		/* Had to read the page from swap area: Major fault */
@@ -1029,7 +1030,8 @@ static int do_swap_page(struct mm_struct * mm,
 		spin_unlock(&mm->page_table_lock);
 		unlock_page(page);
 		page_cache_release(page);
-		return VM_FAULT_MINOR;
+		ret = VM_FAULT_MINOR;
+		goto out;
 	}
 
 	/* The page isn't present yet, go ahead with the fault. */
@@ -1053,6 +1055,7 @@ static int do_swap_page(struct mm_struct * mm,
 	update_mmu_cache(vma, address, pte);
 	pte_unmap(page_table);
 	spin_unlock(&mm->page_table_lock);
+out:
 	return ret;
 }