The patch titled
Subject: mm, thp: always specify disabled vmas as nh in smaps
has been added to the -mm tree. Its filename is
mm-thp-always-specify-disabled-vmas-as-nh-in-smaps.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-thp-always-specify-disabled-vmas-as-nh-in-smaps.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-always-specify-disabled-vmas-as-nh-in-smaps.patch
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------------------------------------------------------
From: David Rientjes <rientjes@xxxxxxxxxx>
Subject: mm, thp: always specify disabled vmas as nh in smaps
1860033237d4 ("mm: make PR_SET_THP_DISABLE immediately active") introduced
a regression in that userspace cannot always determine the set of vmas
where thp is disabled.
Userspace relies on the "nh" flag being emitted as part of /proc/pid/smaps
to determine if a vma has been disabled from being backed by hugepages.
Previous to this commit, prctl(PR_SET_THP_DISABLE, 1) would cause thp to
be disabled and emit "nh" as a flag for the corresponding vmas as part of
/proc/pid/smaps. After the commit, thp is disabled by means of an mm flag
and "nh" is not emitted.
This causes smaps parsing libraries to assume a vma is enabled for thp and
ends up puzzling the user on why its memory is not backed by thp.
This also clears the "hg" flag to make the behavior of MADV_HUGEPAGE and
PR_SET_THP_DISABLE definitive.
Link: http://lkml.kernel.org/r/alpine.DEB.2.21.1809251449060.96762@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 1860033237d4 ("mm: make PR_SET_THP_DISABLE immediately active")
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/filesystems/proc.txt | 7 ++++++-
fs/proc/task_mmu.c | 14 +++++++++++++-
2 files changed, 19 insertions(+), 2 deletions(-)
--- a/Documentation/filesystems/proc.txt~mm-thp-always-specify-disabled-vmas-as-nh-in-smaps
+++ a/Documentation/filesystems/proc.txt
@@ -491,9 +491,14 @@ manner. The codes are the following:
sd - soft-dirty flag
mm - mixed map area
hg - huge page advise flag
- nh - no-huge page advise flag
+ nh - no-huge page advise flag [*]
mg - mergable advise flag
+ [*] A process mapping may be advised to not be backed by transparent hugepages
+ by either madvise(MADV_NOHUGEPAGE) or prctl(PR_SET_THP_DISABLE). See
+ Documentation/admin-guide/mm/transhuge.rst for system-wide and process
+ mapping policies.
+
Note that there is no guarantee that every flag and associated mnemonic will
be present in all further kernel releases. Things get changed, the flags may
be vanished or the reverse -- new added.
--- a/fs/proc/task_mmu.c~mm-thp-always-specify-disabled-vmas-as-nh-in-smaps
+++ a/fs/proc/task_mmu.c
@@ -653,13 +653,25 @@ static void show_smap_vma_flags(struct s
#endif
#endif /* CONFIG_ARCH_HAS_PKEYS */
};
+ unsigned long flags = vma->vm_flags;
size_t i;
+ /*
+ * Disabling thp is possible through both MADV_NOHUGEPAGE and
+ * PR_SET_THP_DISABLE. Both historically used VM_NOHUGEPAGE. Since
+ * the introduction of MMF_DISABLE_THP, however, userspace needs the
+ * ability to detect vmas where thp is not eligible in the same manner.
+ */
+ if (vma->vm_mm && test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags)) {
+ flags &= ~VM_HUGEPAGE;
+ flags |= VM_NOHUGEPAGE;
+ }
+
seq_puts(m, "VmFlags: ");
for (i = 0; i < BITS_PER_LONG; i++) {
if (!mnemonics[i][0])
continue;
- if (vma->vm_flags & (1UL << i)) {
+ if (flags & (1UL << i)) {
seq_putc(m, mnemonics[i][0]);
seq_putc(m, mnemonics[i][1]);
seq_putc(m, ' ');
_
Patches currently in -mm which might be from rientjes@xxxxxxxxxx are
mm-thp-always-specify-disabled-vmas-as-nh-in-smaps.patch
