Messages in this thread Patch in this message |  | | Date | Mon, 24 Sep 2018 10:55:05 -0700 (PDT) | From | David Rientjes <> | Subject | [patch] mm, thp: always specify ineligible vmas as nh in smaps |
| |
Commit 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 ineligible.
Userspace relies on the "nh" flag being emitted as part of /proc/pid/smaps to determine if a vma is eligible to be 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 eligible for thp and ends up puzzling the user on why its memory is not backed by thp.
Signed-off-by: David Rientjes <rientjes@google.com> --- fs/proc/task_mmu.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -653,13 +653,23 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma) #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_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, ' ');
|  |