4.1.28 Fix bad backport of 8f182270 "mm/swap.c: flush lru pvecs on compound page arrival"

When I pulled in 4.1.28 into my stable 4.1-rt tree and ran the tests,
it crashed with a severe OOM killing everything. I then tested 4.1.28
without -rt and it had the same issue. I did a bisect between 4.1.27
and 4.1.28 and found that the bug started at:

commit 8f182270 "mm/swap.c: flush lru pvecs on compound page
arrival"

Looking at that patch and what's in mainline, I see that there's a
mismatch in one of the hunks:

Mainline:

@@ -391,9 +391,8 @@ static void __lru_cache_add(struct page *page)
        struct pagevec *pvec = &get_cpu_var(lru_add_pvec);

        get_page(page);
-       if (!pagevec_space(pvec))
+       if (!pagevec_add(pvec, page) || PageCompound(page))
                __pagevec_lru_add(pvec);
-       pagevec_add(pvec, page);
        put_cpu_var(lru_add_pvec);
 }

Stable 4.1.28:

@@ -631,9 +631,8 @@ static void __lru_cache_add(struct page *page)
        struct pagevec *pvec = &get_cpu_var(lru_add_pvec);

        page_cache_get(page);
-       if (!pagevec_space(pvec))
+       if (!pagevec_space(pvec) || PageCompound(page))
                __pagevec_lru_add(pvec);
-       pagevec_add(pvec, page);
        put_cpu_var(lru_add_pvec);
 }

Where mainline replace pagevec_space() with pagevec_add, and stable did
not.

Fixing this makes the OOM go away.

Note, 3.18 has the same bug.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>

mm/swap.c

@@ -631,7 +631,7 @@ static void __lru_cache_add(struct page *page)
 	struct pagevec *pvec = &get_cpu_var(lru_add_pvec);
 
 	page_cache_get(page);
-	if (!pagevec_space(pvec) || PageCompound(page))
+	if (!pagevec_add(pvec, page) || PageCompound(page))
 		__pagevec_lru_add(pvec);
 	put_cpu_var(lru_add_pvec);
 }