Damn, David somehow didn't make it to the CC list. Sorry about that.
On Tue 20-11-18 11:35:15, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> David Rientjes has reported that 1860033237d4 ("mm: make
> PR_SET_THP_DISABLE immediately active") has changed the way how
> we report THPable VMAs to the userspace. Their monitoring tool is
> triggering false alarms on PR_SET_THP_DISABLE tasks because it considers
> an insufficient THP usage as a memory fragmentation resp. memory
> pressure issue.
>
> Before the said commit each newly created VMA inherited VM_NOHUGEPAGE
> flag and that got exposed to the userspace via /proc/<pid>/smaps file.
> This implementation had its downsides as explained in the commit message
> but it is true that the userspace doesn't have any means to query for
> the process wide THP enabled/disabled status.
>
> PR_SET_THP_DISABLE is a process wide flag so it makes a lot of sense
> to export in the process wide context rather than per-vma. Introduce
> a new field to /proc/<pid>/status which export this status. If
> PR_SET_THP_DISABLE is used then it reports false same as when the THP is
> not compiled in. It doesn't consider the global THP status because we
> already export that information via sysfs
>
> Fixes: 1860033237d4 ("mm: make PR_SET_THP_DISABLE immediately active")
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> Documentation/filesystems/proc.txt | 3 +++
> fs/proc/array.c | 10 ++++++++++
> 2 files changed, 13 insertions(+)
>
> diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
> index 06562bab509a..7995e9322889 100644
> --- a/Documentation/filesystems/proc.txt
> +++ b/Documentation/filesystems/proc.txt
> @@ -182,6 +182,7 @@ For example, to get the status information of a process, all you have to do is
> VmSwap: 0 kB
> HugetlbPages: 0 kB
> CoreDumping: 0
> + THP_enabled: 1
> Threads: 1
> SigQ: 0/28578
> SigPnd: 0000000000000000
> @@ -256,6 +257,8 @@ Table 1-2: Contents of the status files (as of 4.8)
> HugetlbPages size of hugetlb memory portions
> CoreDumping process's memory is currently being dumped
> (killing the process may lead to a corrupted core)
> + THP_enabled process is allowed to use THP (returns 0 when
> + PR_SET_THP_DISABLE is set on the process
> Threads number of threads
> SigQ number of signals queued/max. number for queue
> SigPnd bitmap of pending signals for the thread
> diff --git a/fs/proc/array.c b/fs/proc/array.c
> index 0ceb3b6b37e7..9d428d5a0ac8 100644
> --- a/fs/proc/array.c
> +++ b/fs/proc/array.c
> @@ -392,6 +392,15 @@ static inline void task_core_dumping(struct seq_file *m, struct mm_struct *mm)
> seq_putc(m, '\n');
> }
>
> +static inline void task_thp_status(struct seq_file *m, struct mm_struct *mm)
> +{
> + bool thp_enabled = IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE);
> +
> + if (thp_enabled)
> + thp_enabled = !test_bit(MMF_DISABLE_THP, &mm->flags);
> + seq_printf(m, "THP_enabled:\t%d\n", thp_enabled);
> +}
> +
> int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
> struct pid *pid, struct task_struct *task)
> {
> @@ -406,6 +415,7 @@ int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
> if (mm) {
> task_mem(m, mm);
> task_core_dumping(m, mm);
> + task_thp_status(m, mm);
> mmput(mm);
> }
> task_sig(m, task);
> --
> 2.19.1
--
Michal Hocko
SUSE Labs
