mm: memcontrol: clean up reclaim size variable use in try_charge()

Charge reclaim and OOM currently use the charge batch variable, but
batching is already disabled at that point.  To simplify the charge
logic, the batch variable is reset to the original request size when
reclaim is entered, so it's functionally equal, but it's misleading.

Switch reclaim/OOM to nr_pages, which is the original request size.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -2612,7 +2612,7 @@ static int mem_cgroup_try_charge(struct mem_cgroup *memcg,
 
 	nr_reclaimed = mem_cgroup_reclaim(mem_over_limit, gfp_mask, flags);
 
-	if (mem_cgroup_margin(mem_over_limit) >= batch)
+	if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
 		goto retry;
 
 	if (gfp_mask & __GFP_NORETRY)
@@ -2626,7 +2626,7 @@ static int mem_cgroup_try_charge(struct mem_cgroup *memcg,
 	 * unlikely to succeed so close to the limit, and we fall back
 	 * to regular pages anyway in case of failure.
 	 */
-	if (nr_reclaimed && batch <= (1 << PAGE_ALLOC_COSTLY_ORDER))
+	if (nr_reclaimed && nr_pages <= (1 << PAGE_ALLOC_COSTLY_ORDER))
 		goto retry;
 	/*
 	 * At task move, charge accounts can be doubly counted. So, it's
@@ -2644,7 +2644,7 @@ static int mem_cgroup_try_charge(struct mem_cgroup *memcg,
 	if (fatal_signal_pending(current))
 		goto bypass;
 
-	mem_cgroup_oom(mem_over_limit, gfp_mask, get_order(batch));
+	mem_cgroup_oom(mem_over_limit, gfp_mask, get_order(nr_pages));
 nomem:
 	if (!(gfp_mask & __GFP_NOFAIL))
 		return -ENOMEM;