mm: memcontrol: use "max" instead of "infinity" in control knobs

The memcg control knobs indicate the highest possible value using the
symbolic name "infinity", which is long and awkward to type.

Switch to the string "max", which is just as descriptive but shorter and
sweeter.

This changes a user interface, so do it before the release and before
the development flag is dropped from the default hierarchy.

Signed-off-by: Johannes Weiner <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Tejun Heo <[e-mail]>
Cc: Vladimir Davydov <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/cgroups/unified-hierarchy.txt

···
   be understood as an underflow into the highest possible value, -2 or
   -10M etc. do not work, so it's not consistent.
 
-  memory.low, memory.high, and memory.max will use the string
-  "infinity" to indicate and set the highest possible value.
+  memory.low, memory.high, and memory.max will use the string "max" to
+  indicate and set the highest possible value.
 
 5. Planned Changes
 

mm/memcontrol.c

···
 	unsigned long low = ACCESS_ONCE(memcg->low);
 
 	if (low == PAGE_COUNTER_MAX)
-		seq_puts(m, "infinity\n");
+		seq_puts(m, "max\n");
 	else
 		seq_printf(m, "%llu\n", (u64)low * PAGE_SIZE);
 
···
 	int err;
 
 	buf = strstrip(buf);
-	err = page_counter_memparse(buf, "infinity", &low);
+	err = page_counter_memparse(buf, "max", &low);
 	if (err)
 		return err;
 
···
 	unsigned long high = ACCESS_ONCE(memcg->high);
 
 	if (high == PAGE_COUNTER_MAX)
-		seq_puts(m, "infinity\n");
+		seq_puts(m, "max\n");
 	else
 		seq_printf(m, "%llu\n", (u64)high * PAGE_SIZE);
 
···
 	int err;
 
 	buf = strstrip(buf);
-	err = page_counter_memparse(buf, "infinity", &high);
+	err = page_counter_memparse(buf, "max", &high);
 	if (err)
 		return err;
 
···
 	unsigned long max = ACCESS_ONCE(memcg->memory.limit);
 
 	if (max == PAGE_COUNTER_MAX)
-		seq_puts(m, "infinity\n");
+		seq_puts(m, "max\n");
 	else
 		seq_printf(m, "%llu\n", (u64)max * PAGE_SIZE);
 
···
 	int err;
 
 	buf = strstrip(buf);
-	err = page_counter_memparse(buf, "infinity", &max);
+	err = page_counter_memparse(buf, "max", &max);
 	if (err)
 		return err;