[PATCH linux-next v4] ksm: add ksm involvement information for each process

[<xu.xin16@xxxxxxxxxx>]

From: xu xin <xu.xin16@xxxxxxxxxx>

In /proc/<pid>/ksm_stat, Add two extra ksm involvement items including
KSM_mergeable and KSM_merge_any. It helps administrators to
better know the system's KSM behavior at process level.

KSM_mergeable: yes/no
	whether any VMAs of the process'mm are currently applicable to KSM.

KSM_merge_any: yes/no
	whether the process'mm is added by prctl() into the candidate list
	of KSM or not, and fully enabled at process level.

Changelog
=========
v3 -> v4:
    1. Keep the name of ksm items consistent in /proc/pid/ksm_stat.
	   * KSM_mergeable -> ksm_mergeable
	   * KSM_merge_any -> ksm_merge_any
    2. Hold the read lock of mmap while calling ksm_process_mergeable()
    Suggested-by:
    https://lore.kernel.org/all/cec0ed06-b5d0-45aa-ad2b-eaca6dd7bacb@xxxxxxxxxx/

v2 -> v3:
        Update the KSM_mergeable getting method: loop up if any vma is
        mergeable to KSM.
		https://lore.kernel.org/all/bc0e1cdd-2d9d-437c-8fc9-4df0e13c48c0@xxxxxxxxxx/

v1 -> v2:
        replace the internal flag names with straightforward strings.
        * MMF_VM_MERGEABLE -> KSM_mergeable
        * MMF_VM_MERGE_ANY -> KSM_merge_any

Signed-off-by: xu xin <xu.xin16@xxxxxxxxxx>
Cc: Wang Yaxin <wang.yaxin@xxxxxxxxxx>
---
 fs/proc/base.c      | 11 +++++++++++
 include/linux/ksm.h |  1 +
 mm/ksm.c            | 19 +++++++++++++++++++
 3 files changed, 31 insertions(+)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 0edf14a9840e..a50b222a5917 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3269,6 +3269,7 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns,
 				struct pid *pid, struct task_struct *task)
 {
 	struct mm_struct *mm;
+	int ret = 0;

 	mm = get_task_mm(task);
 	if (mm) {
@@ -3276,6 +3277,16 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns,
 		seq_printf(m, "ksm_zero_pages %ld\n", mm_ksm_zero_pages(mm));
 		seq_printf(m, "ksm_merging_pages %lu\n", mm->ksm_merging_pages);
 		seq_printf(m, "ksm_process_profit %ld\n", ksm_process_profit(mm));
+		seq_printf(m, "ksm_merge_any: %s\n",
+				test_bit(MMF_VM_MERGE_ANY, &mm->flags) ? "yes" : "no");
+		ret = mmap_read_lock_killable(mm);
+		if (ret) {
+			mmput(mm);
+			return ret;
+		}
+		seq_printf(m, "ksm_mergeable: %s\n",
+				ksm_process_mergeable(mm) ? "yes" : "no");
+		mmap_read_unlock(mm);
 		mmput(mm);
 	}

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 6a53ac4885bb..d73095b5cd96 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -93,6 +93,7 @@ void folio_migrate_ksm(struct folio *newfolio, struct folio *folio);
 void collect_procs_ksm(const struct folio *folio, const struct page *page,
 		struct list_head *to_kill, int force_early);
 long ksm_process_profit(struct mm_struct *);
+bool ksm_process_mergeable(struct mm_struct *mm);

 #else  /* !CONFIG_KSM */

diff --git a/mm/ksm.c b/mm/ksm.c
index 7ac59cde626c..e87af149d5ee 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -3263,6 +3263,25 @@ static void wait_while_offlining(void)
 #endif /* CONFIG_MEMORY_HOTREMOVE */

 #ifdef CONFIG_PROC_FS
+/*
+ * The process is mergeable only if any VMA (and which) is currently
+ * applicable to KSM.
+ *
+ * The mmap lock must be held in read mode.
+ */
+bool ksm_process_mergeable(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+
+	mmap_assert_locked(mm);
+	VMA_ITERATOR(vmi, mm, 0);
+	for_each_vma(vmi, vma)
+		if (vma->vm_flags & VM_MERGEABLE)
+			return true;
+
+	return false;
+}
+
 long ksm_process_profit(struct mm_struct *mm)
 {
 	return (long)(mm->ksm_merging_pages + mm_ksm_zero_pages(mm)) * PAGE_SIZE -
-- 
2.15.2