mm: khugepaged: recalculate min_free_kbytes after stopping khugepaged

When initializing transparent huge pages, min_free_kbytes would be
calculated according to what khugepaged expected.

So when transparent huge pages get disabled, min_free_kbytes should be
recalculated instead of the higher value set by khugepaged.

Link: https://lkml.kernel.org/r/1633937809-16558-1-git-send-email-liangcaifan19@gmail.com
Signed-off-by: Liangcai Fan <liangcaifan19@gmail.com>
Signed-off-by: Chunyan Zhang <zhang.lyra@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mm.h

@@ -2453,6 +2453,7 @@ extern void memmap_init_range(unsigned long, int, unsigned long,
 		unsigned long, unsigned long, enum meminit_context,
 		struct vmem_altmap *, int migratetype);
 extern void setup_per_zone_wmarks(void);
+extern void calculate_min_free_kbytes(void);
 extern int __meminit init_per_zone_wmark_min(void);
 extern void mem_init(void);
 extern void __init mmap_init(void);

mm/khugepaged.c

@@ -2299,6 +2299,11 @@ static void set_recommended_min_free_kbytes(void)
 	int nr_zones = 0;
 	unsigned long recommended_min;
 
+	if (!khugepaged_enabled()) {
+		calculate_min_free_kbytes();
+		goto update_wmarks;
+	}
+
 	for_each_populated_zone(zone) {
 		/*
 		 * We don't need to worry about fragmentation of
@@ -2334,6 +2339,8 @@ static void set_recommended_min_free_kbytes(void)
 
 		min_free_kbytes = recommended_min;
 	}
+
+update_wmarks:
 	setup_per_zone_wmarks();
 }
 
@@ -2355,12 +2362,11 @@ int start_stop_khugepaged(void)
 
 		if (!list_empty(&khugepaged_scan.mm_head))
 			wake_up_interruptible(&khugepaged_wait);
-
-		set_recommended_min_free_kbytes();
 	} else if (khugepaged_thread) {
 		kthread_stop(khugepaged_thread);
 		khugepaged_thread = NULL;
 	}
+	set_recommended_min_free_kbytes();
 fail:
 	mutex_unlock(&khugepaged_mutex);
 	return err;

mm/page_alloc.c

@@ -8469,7 +8469,7 @@ void setup_per_zone_wmarks(void)
  * 8192MB:	11584k
  * 16384MB:	16384k
  */
-int __meminit init_per_zone_wmark_min(void)
+void calculate_min_free_kbytes(void)
 {
 	unsigned long lowmem_kbytes;
 	int new_min_free_kbytes;
@@ -8483,6 +8483,11 @@ int __meminit init_per_zone_wmark_min(void)
 		pr_warn("min_free_kbytes is not updated to %d because user defined value %d is preferred\n",
 				new_min_free_kbytes, user_min_free_kbytes);
 
+}
+
+int __meminit init_per_zone_wmark_min(void)
+{
+	calculate_min_free_kbytes();
 	setup_per_zone_wmarks();
 	refresh_zone_stat_thresholds();
 	setup_per_zone_lowmem_reserve();