On Tue, 3 Dec 2024 19:26:33 +0800 (CST) <xu.xin16@xxxxxxxxxx> wrote:
> 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.
It's hard for me to judge the usefulness of this. Please tell us more:
usage examples, what actions have been taken using this information, etc.
> KSM_mergeable: yes/no
> whether any VMAs of the process'mm are currently applicable to KSM.
Could we simply display VM_MERGEABLE in /proc/<pid>/maps?
> 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.
>
> ...
>
> fs/proc/base.c | 11 +++++++++++
> include/linux/ksm.h | 1 +
> mm/ksm.c | 19 +++++++++++++++++++
Documentation/admin-guide/mm/ksm.rst will require an update please.
>
> ...
>
> --- 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);
Could do the locking in ksm_process_mergeable()?
> + if (ret) {
> + mmput(mm);
> + return ret;
> + }
> + seq_printf(m, "ksm_mergeable: %s\n",
> + ksm_process_mergeable(mm) ? "yes" : "no");
Calling seq_printf() after the mmap_read_unlock() would be a little
more scalable.
> + mmap_read_unlock(mm);
> mmput(mm);
> }
>
> ...
>
> --- 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.
That sentence needs revisiting, please.
> + * 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;
> +}
