Re: [patch] mm, thp: always specify ineligible vmas as nh in smaps

On Mon, 24 Sep 2018, Vlastimil Babka wrote:

quoted

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;

Should it also clear VM_HUGEPAGE? In case MMF_DISABLE_THP overrides a
madvise(MADV_HUGEPAGE)'d vma? (I expect it does?)

Good point, I think that is should because MMF_DISABLE_THP will override 
VM_HUGEPAGE.  It looks like the Documentation file is still referencing 
both as advise flags and doesn't address PR_SET_THP_DISABLE.  Let me send 
a v2 with a Documentation update and your suggested fix.  Thanks 
Vlastimil!

quoted

+
 	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, ' ');