memcg: never OOM when charging huge pages

Huge page coverage should obviously have less priority than the continued
execution of a process.

Never kill a process when charging it a huge page fails.  Instead, give up
after the first failed reclaim attempt and fall back to regular pages.
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -2351,13 +2351,19 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
 				gfp_t gfp_mask, enum charge_type ctype)
 {
 	struct mem_cgroup *mem = NULL;
+	int page_size = PAGE_SIZE;
 	struct page_cgroup *pc;
+	bool oom = true;
 	int ret;
-	int page_size = PAGE_SIZE;
 
 	if (PageTransHuge(page)) {
 		page_size <<= compound_order(page);
 		VM_BUG_ON(!PageTransHuge(page));
+		/*
+		 * Never OOM-kill a process for a huge page.  The
+		 * fault handler will fall back to regular pages.
+		 */
+		oom = false;
 	}
 
 	pc = lookup_page_cgroup(page);
@@ -2366,7 +2372,7 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
 		return 0;
 	prefetchw(pc);
 
-	ret = __mem_cgroup_try_charge(mm, gfp_mask, &mem, true, page_size);
+	ret = __mem_cgroup_try_charge(mm, gfp_mask, &mem, oom, page_size);
 	if (ret || !mem)
 		return ret;