On 9/16/2020 12:59 AM, Michal Hocko wrote:
On Tue 15-09-20 14:10:58, Vijay Balakrishna wrote:
set_recommended_min_free_kbytes need to honor min_free_kbytes set by the
user. Post start-of-day THP enable or memory hotplug operations can
lose user specified min_free_kbytes, in particular when it is higher than
calculated recommended value. Also modifying "recommended_min" variable
type to "int" from "unsigned long" to avoid undesired result noticed
during testing. It is due to comparing "unsigned long" with "int" type.
Signed-off-by: Vijay Balakrishna <vijayb@xxxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
---
mm/khugepaged.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 4f7107476a6f..b4b753ba411a 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2253,7 +2253,7 @@ static void set_recommended_min_free_kbytes(void)
{
struct zone *zone;
int nr_zones = 0;
- unsigned long recommended_min;
+ int recommended_min;
for_each_populated_zone(zone) {
/*
@@ -2280,12 +2280,12 @@ static void set_recommended_min_free_kbytes(void)
/* don't ever allow to reserve more than 5% of the lowmem */
recommended_min = min(recommended_min,
- (unsigned long) nr_free_buffer_pages() / 20);
+ (int) nr_free_buffer_pages() / 20);
nr_free_buffer_pages can oveflow in int on very large machines.
Good point. I will address it.
recommended_min <<= (PAGE_SHIFT-10);
- if (recommended_min > min_free_kbytes) {
+ if (recommended_min > user_min_free_kbytes) {
This can decrease the size theoretically. Because user_min_free_kbytes
is -1 by default and recommended_min might be <= min_free_kbytes.
You need to check both. Also can we make user_min_free_kbytes 0 by
default? From a quick look, nobody should really care.
Let me rework.
Thanks,
Vijay
if (user_min_free_kbytes >= 0)
- pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
+ pr_info("raising min_free_kbytes from %d to %d to help transparent hugepage allocations\n",
min_free_kbytes, recommended_min);
min_free_kbytes = recommended_min;
--
2.28.0
