mm: vmscan: naming fixes: global_reclaim() and sane_reclaim()

Seven years after introducing the global_reclaim() function, I still have
to double take when reading a callsite.  I don't know how others do it,
this is a terrible name.

Invert the meaning and rename it to cgroup_reclaim().

[ After all, "global reclaim" is just regular reclaim invoked from the
  page allocator. It's reclaim on behalf of a cgroup limit that is a
  special case of reclaim, and should be explicit - not the reverse. ]

sane_reclaim() isn't very descriptive either: it tests whether we can use
the regular writeback throttling - available during regular page reclaim
or cgroup2 limit reclaim - or need to use the broken
wait_on_page_writeback() method.  Use "writeback_throttling_sane()".

Link: http://lkml.kernel.org/r/20191022144803.302233-5-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Roman Gushchin <guro@fb.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -239,13 +239,13 @@ static void unregister_memcg_shrinker(struct shrinker *shrinker)
 	up_write(&shrinker_rwsem);
 }
 
-static bool global_reclaim(struct scan_control *sc)
+static bool cgroup_reclaim(struct scan_control *sc)
 {
-	return !sc->target_mem_cgroup;
+	return sc->target_mem_cgroup;
 }
 
 /**
- * sane_reclaim - is the usual dirty throttling mechanism operational?
+ * writeback_throttling_sane - is the usual dirty throttling mechanism available?
  * @sc: scan_control in question
  *
  * The normal page dirty throttling mechanism in balance_dirty_pages() is
@@ -257,11 +257,9 @@ static bool global_reclaim(struct scan_control *sc)
  * This function tests whether the vmscan currently in progress can assume
  * that the normal dirty throttling mechanism is operational.
  */
-static bool sane_reclaim(struct scan_control *sc)
+static bool writeback_throttling_sane(struct scan_control *sc)
 {
-	struct mem_cgroup *memcg = sc->target_mem_cgroup;
+	if (!cgroup_reclaim(sc))
-
-	if (!memcg)
 		return true;
 #ifdef CONFIG_CGROUP_WRITEBACK
 	if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
@@ -302,12 +300,12 @@ static void unregister_memcg_shrinker(struct shrinker *shrinker)
 {
 }
 
-static bool global_reclaim(struct scan_control *sc)
+static bool cgroup_reclaim(struct scan_control *sc)
 {
-	return true;
+	return false;
 }
 
-static bool sane_reclaim(struct scan_control *sc)
+static bool writeback_throttling_sane(struct scan_control *sc)
 {
 	return true;
 }
@@ -1227,7 +1225,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 				goto activate_locked;
 
 			/* Case 2 above */
-			} else if (sane_reclaim(sc) ||
+			} else if (writeback_throttling_sane(sc) ||
 			    !PageReclaim(page) || !may_enter_fs) {
 				/*
 				 * This is slightly racy - end_page_writeback()
@@ -1821,7 +1819,7 @@ static int too_many_isolated(struct pglist_data *pgdat, int file,
 	if (current_is_kswapd())
 		return 0;
 
-	if (!sane_reclaim(sc))
+	if (!writeback_throttling_sane(sc))
 		return 0;
 
 	if (file) {
@@ -1971,7 +1969,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 	reclaim_stat->recent_scanned[file] += nr_taken;
 
 	item = current_is_kswapd() ? PGSCAN_KSWAPD : PGSCAN_DIRECT;
-	if (global_reclaim(sc))
+	if (!cgroup_reclaim(sc))
 		__count_vm_events(item, nr_scanned);
 	__count_memcg_events(lruvec_memcg(lruvec), item, nr_scanned);
 	spin_unlock_irq(&pgdat->lru_lock);
@@ -1985,7 +1983,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 	spin_lock_irq(&pgdat->lru_lock);
 
 	item = current_is_kswapd() ? PGSTEAL_KSWAPD : PGSTEAL_DIRECT;
-	if (global_reclaim(sc))
+	if (!cgroup_reclaim(sc))
 		__count_vm_events(item, nr_reclaimed);
 	__count_memcg_events(lruvec_memcg(lruvec), item, nr_reclaimed);
 	reclaim_stat->recent_rotated[0] += stat.nr_activate[0];
@@ -2309,7 +2307,7 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
 	 * using the memory controller's swap limit feature would be
 	 * too expensive.
 	 */
-	if (!global_reclaim(sc) && !swappiness) {
+	if (cgroup_reclaim(sc) && !swappiness) {
 		scan_balance = SCAN_FILE;
 		goto out;
 	}
@@ -2333,7 +2331,7 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
 	 * thrashing file LRU becomes infinitely more attractive than
 	 * anon pages.  Try to detect this based on file LRU size.
 	 */
-	if (global_reclaim(sc)) {
+	if (!cgroup_reclaim(sc)) {
 		unsigned long pgdatfile;
 		unsigned long pgdatfree;
 		int z;
@@ -2564,7 +2562,7 @@ static void shrink_node_memcg(struct pglist_data *pgdat, struct mem_cgroup *memc
 	 * abort proportional reclaim if either the file or anon lru has already
 	 * dropped to zero at the first pass.
 	 */
-	scan_adjusted = (global_reclaim(sc) && !current_is_kswapd() &&
+	scan_adjusted = (!cgroup_reclaim(sc) && !current_is_kswapd() &&
 			 sc->priority == DEF_PRIORITY);
 
 	blk_start_plug(&plug);
@@ -2853,7 +2851,7 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
 		 * Legacy memcg will stall in page writeback so avoid forcibly
 		 * stalling in wait_iff_congested().
 		 */
-		if (!global_reclaim(sc) && sane_reclaim(sc) &&
+		if (cgroup_reclaim(sc) && writeback_throttling_sane(sc) &&
 		    sc->nr.dirty && sc->nr.dirty == sc->nr.congested)
 			set_memcg_congestion(pgdat, root, true);
 
@@ -2948,7 +2946,7 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
 		 * Take care memory controller reclaiming has small influence
 		 * to global LRU.
 		 */
-		if (global_reclaim(sc)) {
+		if (!cgroup_reclaim(sc)) {
 			if (!cpuset_zone_allowed(zone,
 						 GFP_KERNEL | __GFP_HARDWALL))
 				continue;
@@ -3048,7 +3046,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
 retry:
 	delayacct_freepages_start();
 
-	if (global_reclaim(sc))
+	if (!cgroup_reclaim(sc))
 		__count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1);
 
 	do {