try_charge_memcg() does a lot. It charges the page counters, reclaims
when a limit is hit, may call the OOM killer, and at the end it checks
and enforces memory.high. Move the memory.high part into a new function,
memcg_enforce_high(), so that try_charge_memcg() is shorter and the
memory.high code is easier to read and change.

The code and its comments move as they are. The only difference is that
the new function gets allow_spinning from gfp_mask itself.

No functional change.
---
 mm/memcontrol.c | 125 ++++++++++++++++++++++++++----------------------
 1 file changed, 69 insertions(+), 56 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index aad0498a7bd6..20c5dfe1a894 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2696,6 +2696,74 @@ void __mem_cgroup_handle_over_high(gfp_t gfp_mask)
 	css_put(&memcg->css);
 }
 
+/*
+ * Called after @nr_pages were charged to @memcg. If @memcg or one of its
+ * ancestors is over memory.high or memory.swap.high, start reclaim or slow
+ * down the task.
+ */
+static void memcg_enforce_high(struct mem_cgroup *memcg, unsigned int nr_pages,
+			       gfp_t gfp_mask)
+{
+	bool allow_spinning = gfpflags_allow_spinning(gfp_mask);
+
+	/*
+	 * If the hierarchy is above the normal consumption range, schedule
+	 * reclaim on returning to userland.  We can perform reclaim here
+	 * if __GFP_RECLAIM but let's always punt for simplicity and so that
+	 * GFP_KERNEL can consistently be used during reclaim.  @memcg is
+	 * not recorded as it most likely matches current's and won't
+	 * change in the meantime.  As high limit is checked again before
+	 * reclaim, the cost of mismatch is negligible.
+	 */
+	do {
+		bool mem_high, swap_high;
+
+		mem_high = page_counter_read(&memcg->memory) >
+			READ_ONCE(memcg->memory.high);
+		swap_high = page_counter_read(&memcg->swap) >
+			READ_ONCE(memcg->swap.high);
+
+		/* Don't bother a random interrupted task */
+		if (!in_task()) {
+			if (mem_high) {
+				if (allow_spinning)
+					schedule_work(&memcg->high_work);
+				else
+					irq_work_queue(&memcg->high_irq_work);
+				break;
+			}
+			continue;
+		}
+
+		if (mem_high || swap_high) {
+			/*
+			 * The allocating tasks in this cgroup will need to do
+			 * reclaim or be throttled to prevent further growth
+			 * of the memory or swap footprints.
+			 *
+			 * Target some best-effort fairness between the tasks,
+			 * and distribute reclaim work and delay penalties
+			 * based on how much each task is actually allocating.
+			 */
+			current->memcg_nr_pages_over_high += nr_pages;
+			set_notify_resume(current);
+			break;
+		}
+	} while ((memcg = parent_mem_cgroup(memcg)));
+
+	/*
+	 * Reclaim is set up above to be called from the userland
+	 * return path. But also attempt synchronous reclaim to avoid
+	 * excessive overrun while the task is still inside the
+	 * kernel. If this is successful, the return path will see it
+	 * when it rechecks the overage and simply bail out.
+	 */
+	if (current->memcg_nr_pages_over_high > MEMCG_CHARGE_BATCH &&
+	    !(current->flags & PF_MEMALLOC) &&
+	    gfpflags_allow_blocking(gfp_mask))
+		__mem_cgroup_handle_over_high(gfp_mask);
+}
+
 static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
 			    unsigned int nr_pages)
 {
@@ -2853,62 +2921,7 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	if (batch > nr_pages)
 		refill_stock(memcg, batch - nr_pages);
 
-	/*
-	 * If the hierarchy is above the normal consumption range, schedule
-	 * reclaim on returning to userland.  We can perform reclaim here
-	 * if __GFP_RECLAIM but let's always punt for simplicity and so that
-	 * GFP_KERNEL can consistently be used during reclaim.  @memcg is
-	 * not recorded as it most likely matches current's and won't
-	 * change in the meantime.  As high limit is checked again before
-	 * reclaim, the cost of mismatch is negligible.
-	 */
-	do {
-		bool mem_high, swap_high;
-
-		mem_high = page_counter_read(&memcg->memory) >
-			READ_ONCE(memcg->memory.high);
-		swap_high = page_counter_read(&memcg->swap) >
-			READ_ONCE(memcg->swap.high);
-
-		/* Don't bother a random interrupted task */
-		if (!in_task()) {
-			if (mem_high) {
-				if (allow_spinning)
-					schedule_work(&memcg->high_work);
-				else
-					irq_work_queue(&memcg->high_irq_work);
-				break;
-			}
-			continue;
-		}
-
-		if (mem_high || swap_high) {
-			/*
-			 * The allocating tasks in this cgroup will need to do
-			 * reclaim or be throttled to prevent further growth
-			 * of the memory or swap footprints.
-			 *
-			 * Target some best-effort fairness between the tasks,
-			 * and distribute reclaim work and delay penalties
-			 * based on how much each task is actually allocating.
-			 */
-			current->memcg_nr_pages_over_high += batch;
-			set_notify_resume(current);
-			break;
-		}
-	} while ((memcg = parent_mem_cgroup(memcg)));
-
-	/*
-	 * Reclaim is set up above to be called from the userland
-	 * return path. But also attempt synchronous reclaim to avoid
-	 * excessive overrun while the task is still inside the
-	 * kernel. If this is successful, the return path will see it
-	 * when it rechecks the overage and simply bail out.
-	 */
-	if (current->memcg_nr_pages_over_high > MEMCG_CHARGE_BATCH &&
-	    !(current->flags & PF_MEMALLOC) &&
-	    gfpflags_allow_blocking(gfp_mask))
-		__mem_cgroup_handle_over_high(gfp_mask);
+	memcg_enforce_high(memcg, batch, gfp_mask);
 	return ret;
 }
 
-- 
2.53.0-Meta