mm, memcg: unify reclaim retry limits with page allocator

Reclaim retries have been set to 5 since the beginning of time in
commit 66e1707 ("Memory controller: add per cgroup LRU and
reclaim").  However, we now have a generally agreed-upon standard for
page reclaim: MAX_RECLAIM_RETRIES (currently 16), added many years later
in commit 0a0337e ("mm, oom: rework oom detection").

In the absence of a compelling reason to declare an OOM earlier in memcg
context than page allocator context, it seems reasonable to supplant
MEM_CGROUP_RECLAIM_RETRIES with MAX_RECLAIM_RETRIES, making the page
allocator and memcg internals more similar in semantics when reclaim
fails to produce results, avoiding premature OOMs or throttling.

Signed-off-by: Chris Down <chris@chrisdown.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <guro@fb.com>
Link: http://lkml.kernel.org/r/da557856c9c7654308eaff4eedc1952a95e8df5f.1594640214.git.chris@chrisdown.name
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -73,9 +73,6 @@ EXPORT_SYMBOL(memory_cgrp_subsys);
 
 struct mem_cgroup *root_mem_cgroup __read_mostly;
 
-/* The number of times we should retry reclaim failures before giving up. */
-#define MEM_CGROUP_RECLAIM_RETRIES	5
-
 /* Socket memory accounting disabled? */
 static bool cgroup_memory_nosocket;
 
@@ -2538,7 +2535,7 @@ void mem_cgroup_handle_over_high(void)
 	unsigned long pflags;
 	unsigned long nr_reclaimed;
 	unsigned int nr_pages = current->memcg_nr_pages_over_high;
-	int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
+	int nr_retries = MAX_RECLAIM_RETRIES;
 	struct mem_cgroup *memcg;
 	bool in_retry = false;
 
@@ -2615,7 +2612,7 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
 		      unsigned int nr_pages)
 {
 	unsigned int batch = max(MEMCG_CHARGE_BATCH, nr_pages);
-	int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
+	int nr_retries = MAX_RECLAIM_RETRIES;
 	struct mem_cgroup *mem_over_limit;
 	struct page_counter *counter;
 	unsigned long nr_reclaimed;
@@ -2734,7 +2731,7 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
 		       get_order(nr_pages * PAGE_SIZE));
 	switch (oom_status) {
 	case OOM_SUCCESS:
-		nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
+		nr_retries = MAX_RECLAIM_RETRIES;
 		goto retry;
 	case OOM_FAILED:
 		goto force;
@@ -3414,7 +3411,7 @@ static inline bool memcg_has_children(struct mem_cgroup *memcg)
  */
 static int mem_cgroup_force_empty(struct mem_cgroup *memcg)
 {
-	int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
+	int nr_retries = MAX_RECLAIM_RETRIES;
 
 	/* we call try-to-free pages for make this cgroup empty */
 	lru_add_drain_all();
@@ -6235,7 +6232,7 @@ static ssize_t memory_high_write(struct kernfs_open_file *of,
 				 char *buf, size_t nbytes, loff_t off)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
-	unsigned int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
+	unsigned int nr_retries = MAX_RECLAIM_RETRIES;
 	bool drained = false;
 	unsigned long high;
 	int err;
@@ -6283,7 +6280,7 @@ static ssize_t memory_max_write(struct kernfs_open_file *of,
 				char *buf, size_t nbytes, loff_t off)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
-	unsigned int nr_reclaims = MEM_CGROUP_RECLAIM_RETRIES;
+	unsigned int nr_reclaims = MAX_RECLAIM_RETRIES;
 	bool drained = false;
 	unsigned long max;
 	int err;