[PATCH v3 6/6] mm: add sysfs entry to disable splitting underutilized THPs

Usama Arif
2024-08-13T12:03:51Z

If disabled, THPs faulted in or collapsed will not be added to
_deferred_list, and therefore won't be considered for splitting under
memory pressure if underutilized.

Signed-off-by: Usama Arif <usamaarif642@gmail.com>
---
mm/huge_memory.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 6b32b2d4ab1e..b4d72479330d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -74,6 +74,7 @@ static unsigned long deferred_split_count(struct shrinker *shrink,
struct shrink_control *sc);
static unsigned long deferred_split_scan(struct shrinker *shrink,
struct shrink_control *sc);
+static bool split_underutilized_thp = true;

static atomic_t huge_zero_refcount;
struct folio *huge_zero_folio __read_mostly;
@@ -439,6 +440,27 @@ static ssize_t hpage_pmd_size_show(struct kobject *kobj,
static struct kobj_attribute hpage_pmd_size_attr =
__ATTR_RO(hpage_pmd_size);

+static ssize_t split_underutilized_thp_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%d\n", split_underutilized_thp);
+}
+
+static ssize_t split_underutilized_thp_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ int err = kstrtobool(buf, &split_underutilized_thp);
+
+ if (err < 0)
+ return err;
+
+ return count;
+}
+
+static struct kobj_attribute split_underutilized_thp_attr = __ATTR(
+ thp_low_util_shrinker, 0644, split_underutilized_thp_show, split_underutilized_thp_store);
+
static struct attribute *hugepage_attr[] = {
&enabled_attr.attr,
&defrag_attr.attr,
@@ -447,6 +469,7 @@ static struct attribute *hugepage_attr[] = {
#ifdef CONFIG_SHMEM
&shmem_enabled_attr.attr,
#endif
+ &split_underutilized_thp_attr.attr,
NULL,
};

@@ -3475,6 +3498,9 @@ void deferred_split_folio(struct folio *folio, bool partially_mapped)
if (folio_order(folio) <= 1)
return;

+ if (!partially_mapped && !split_underutilized_thp)
+ return;
+
/*
* The try_to_unmap() in page reclaim path might reach here too,
* this may cause a race condition to corrupt deferred split queue.
--
2.43.5