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mm, proc: report PR_SET_THP_DISABLE in proc

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David Rientjes has reported that commit 1860033237 ("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: 1860033237 ("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>
This commit is contained in:
Michal Hocko 2018-12-28 00:38:25 -08:00 committed by Linus Torvalds
parent 7635d9cbe8
commit a1400af755
2 changed files with 13 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
Documentation/filesystems/proc.txt
View File

@ -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

10
fs/proc/array.c
View File

@ -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);