[PATCH RFC v2 3/4] mm/ksm: introduce force_madvise knob

Oleksandr Natalenko
2019-05-14T13:17:12Z

Present a new sysfs knob to mark task's anonymous memory as mergeable.

To force merging task's VMAs, its PID is echoed in a write-only file:

# echo PID > /sys/kernel/mm/ksm/force_madvise

Force unmerging is done similarly, but with "minus" sign:

# echo -PID > /sys/kernel/mm/ksm/force_madvise

"0" or "-0" can be used to control the current task.

To achieve this, previously introduced ksm_enter()/ksm_leave() helpers
are used in the "store" handler.

Signed-off-by: Oleksandr Natalenko <oleksandr@redhat.com>
---
mm/ksm.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 68 insertions(+)

diff --git a/mm/ksm.c b/mm/ksm.c
index e9f3901168bb..22c59fb03d3a 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2879,10 +2879,77 @@ static void wait_while_offlining(void)

#define KSM_ATTR_RO(_name) \
static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
+#define KSM_ATTR_WO(_name) \
+ static struct kobj_attribute _name##_attr = __ATTR_WO(_name)
#define KSM_ATTR(_name) \
static struct kobj_attribute _name##_attr = \
__ATTR(_name, 0644, _name##_show, _name##_store)

+static ssize_t force_madvise_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ int err;
+ pid_t pid;
+ bool merge = true;
+ struct task_struct *tsk;
+ struct mm_struct *mm;
+ struct vm_area_struct *vma;
+
+ err = kstrtoint(buf, 10, &pid);
+ if (err)
+ return -EINVAL;
+
+ if (pid < 0) {
+ pid = abs(pid);
+ merge = false;
+ }
+
+ if (!pid && *buf == '-')
+ merge = false;
+
+ rcu_read_lock();
+ if (pid) {
+ tsk = find_task_by_vpid(pid);
+ if (!tsk) {
+ err = -ESRCH;
+ rcu_read_unlock();
+ goto out;
+ }
+ } else {
+ tsk = current;
+ }
+
+ tsk = tsk->group_leader;
+
+ get_task_struct(tsk);
+ rcu_read_unlock();
+
+ mm = get_task_mm(tsk);
+ if (!mm) {
+ err = -EINVAL;
+ goto out_put_task_struct;
+ }
+ down_write(&mm->mmap_sem);
+ vma = mm->mmap;
+ while (vma) {
+ if (merge)
+ ksm_enter(vma->vm_mm, vma, &vma->vm_flags);
+ else
+ ksm_leave(vma, vma->vm_start, vma->vm_end, &vma->vm_flags);
+ vma = vma->vm_next;
+ }
+ up_write(&mm->mmap_sem);
+ mmput(mm);
+
+out_put_task_struct:
+ put_task_struct(tsk);
+
+out:
+ return err ? err : count;
+}
+KSM_ATTR_WO(force_madvise);
+
static ssize_t sleep_millisecs_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
@@ -3185,6 +3252,7 @@ static ssize_t full_scans_show(struct kobject *kobj,
KSM_ATTR_RO(full_scans);

static struct attribute *ksm_attrs[] = {
+ &force_madvise_attr.attr,
&sleep_millisecs_attr.attr,
&pages_to_scan_attr.attr,
&run_attr.attr,
--
2.21.0