Commit a1400af7 authored Dec 28, 2018 by Michal Hocko Committed by Linus Torvalds Dec 28, 2018

mm, proc: report PR_SET_THP_DISABLE in proc

David Rientjes has reported that commit 18600332 ("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

Link: http://lkml.kernel.org/r/20181211143641.3503-4-mhocko@kernel.org


Fixes: 18600332 ("mm: make PR_SET_THP_DISABLE immediately active")
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reported-by: David Rientjes <rientjes@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Paul Oppenheimer <bepvte@gmail.com>
Cc: William Kucharski <william.kucharski@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 7635d9cb

Documentation/filesystems/proc.txt

+3 −0

Original line number	Diff line number	Diff line
		@@ -182,6 +182,7 @@ read the file /proc/PID/status:
		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

fs/proc/array.c

+10 −0

Original line number	Diff line number	Diff line
		@@ -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);

Admin message