Re: [PATCH 0/2] mm->def_flags cleanups (Was: Change khugepaged to respect MMF_THP_DISABLE flag)

[Oleg Nesterov <oleg@redhat.com>]

On 01/22, Oleg Nesterov wrote:
>
> Can't we simply add VM_NOHUGEPAGE into ->def_flags? See the (untested)
> patch below, on top of this series.

And perhaps the patch below makes sense as a separate change, I dunno.


------------------------------------------------------------------------------
Subject: [PATCH] mm: introduce VM_INIT_DEF_MASK

mm_init() always sets new_mm->def_flags = 0. We might want to
inherit some bits like we do with mm->flags.

Add the new VM_INIT_DEF_MASK (currently zero) which acts like
MMF_INIT_MASK for ->def_flags.
---
 include/linux/mm.h |    2 ++
 kernel/fork.c      |   11 ++++++++---
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1cedd00..0a340c9 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -167,6 +167,8 @@ extern unsigned int kobjsize(const void *objp);
  */
 #define VM_SPECIAL (VM_IO | VM_DONTEXPAND | VM_PFNMAP)
 
+#define VM_INIT_DEF_MASK	0
+
 /*
  * mapping from the currently active vm_flags protection bits (the
  * low four bits) to a page protection mask..
diff --git a/kernel/fork.c b/kernel/fork.c
index b84bef7..f6d020b 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -529,8 +529,6 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
 	atomic_set(&mm->mm_count, 1);
 	init_rwsem(&mm->mmap_sem);
 	INIT_LIST_HEAD(&mm->mmlist);
-	mm->flags = (current->mm) ?
-		(current->mm->flags & MMF_INIT_MASK) : default_dump_filter;
 	mm->core_state = NULL;
 	atomic_long_set(&mm->nr_ptes, 0);
 	memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
@@ -538,8 +536,15 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
 	mm_init_aio(mm);
 	mm_init_owner(mm, p);
 
-	if (likely(!mm_alloc_pgd(mm))) {
+	if (current->mm) {
+		mm->flags = current->mm->flags & MMF_INIT_MASK;
+		mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK;
+	} else {
+		mm->flags = default_dump_filter;
 		mm->def_flags = 0;
+	}
+
+	if (likely(!mm_alloc_pgd(mm))) {
 		mmu_notifier_mm_init(mm);
 		return mm;
 	}
-- 
1.5.5.1