alinux: mm, memcg: adjust the latency probe point for memcg direct reclaim

to #26424368

Since there are features other than memcg direct reclaim which also
invoke try_to_free_mem_cgroup_pages, such as zombie memcg reaper, memcg
kswapd, etc,.  Move the latency probe point for memcg direct reclaim
from function try_to_free_mem_cgroup_pages to function try_charge, in
order to distinguish memcg direct reclaim.
Signed-off-by: NXu Yu <xuyu@linux.alibaba.com>
Reviewed-by: NYang Shi <yang.shi@linux.alibaba.com>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>

mm/memcontrol.c

@@ -2544,6 +2544,7 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	bool drained = false;
 	bool oomed = false;
 	enum oom_status oom_status;
+	u64 start;
 
 	if (mem_cgroup_is_root(memcg))
 		return 0;
@@ -2603,8 +2604,11 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
 
 	memcg_memory_event(mem_over_limit, MEMCG_MAX);
 
+	start = ktime_get_ns();
 	nr_reclaimed = try_to_free_mem_cgroup_pages(mem_over_limit, nr_pages,
 						    gfp_mask, may_swap);
+	memcg_lat_stat_update(MEM_LAT_MEMCG_DIRECT_RECLAIM,
+			      (ktime_get_ns() - start));
 
 	if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
 		goto retry;

mm/vmscan.c

@@ -3454,7 +3454,6 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
 	unsigned long pflags;
 	int nid;
 	unsigned int noreclaim_flag;
-	u64 start;
 	struct scan_control sc = {
 		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
 		.gfp_mask = (current_gfp_context(gfp_mask) & GFP_RECLAIM_MASK) |
@@ -3482,14 +3481,11 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
 					    sc.reclaim_idx);
 
 	psi_memstall_enter(&pflags);
-	start = ktime_get_ns();
 	noreclaim_flag = memalloc_noreclaim_save();
 
 	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
 
 	memalloc_noreclaim_restore(noreclaim_flag);
-	memcg_lat_stat_update(MEM_LAT_MEMCG_DIRECT_RECLAIM,
-			      (ktime_get_ns() - start));
 	psi_memstall_leave(&pflags);
 
 	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);