linux-kernel - Re: [PATCH 1/2] hugetlbfs: stop setting VM_DONTDUMP in initializing vma(VM

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Date:	Thu, 28 Mar 2013 14:29:18 -0400
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] hugetlbfs: stop setting VM_DONTDUMP in initializing
 vma(VM_HUGETLB)

On Thu, Mar 28, 2013 at 09:03:16PM +0400, Konstantin Khlebnikov wrote:
> Naoya Horiguchi wrote:
> >Currently we fail to include any data on hugepages into coredump,
> >because VM_DONTDUMP is set on hugetlbfs's vma. This behavior was recently
> >introduced by commit 314e51b98 "mm: kill vma flag VM_RESERVED and
> >mm->reserved_vm counter". This looks to me a serious regression,
> >so let's fix it.
> 
> That was introduced in my patch? Really?
> Here was VM_RESERVED and it had the same effect as VM_DONTDUMP. At least I thought so.

vma_dump_size() does like this (the diff is the one in 314e51b98):

   static unsigned long vma_dump_size(struct vm_area_struct *vma,
   				   unsigned long mm_flags)
   {
   #define FILTER(type)	(mm_flags & (1UL << MMF_DUMP_##type))
   
   	/* always dump the vdso and vsyscall sections */
   	if (always_dump_vma(vma))
   		goto whole;
  
  	if (vma->vm_flags & VM_DONTDUMP)
   		return 0;
   
   	/* Hugetlb memory check */
   	if (vma->vm_flags & VM_HUGETLB) {
   		if ((vma->vm_flags & VM_SHARED) && FILTER(HUGETLB_SHARED))
   			goto whole;
   		if (!(vma->vm_flags & VM_SHARED) && FILTER(HUGETLB_PRIVATE))
   			goto whole;
   	}
   
   	/* Do not dump I/O mapped devices or special mappings */
  -	if (vma->vm_flags & (VM_IO | VM_RESERVED))
  +	if (vma->vm_flags & VM_IO)
   		return 0;

We have hugetlb memory check after VM_DONTDUMP check, so the following
changed the behavior.

  --- a/fs/hugetlbfs/inode.c
  +++ b/fs/hugetlbfs/inode.c
  @@ -110,7 +110,7 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
           * way when do_mmap_pgoff unwinds (may be important on powerpc
           * and ia64).
           */
  -       vma->vm_flags |= VM_HUGETLB | VM_RESERVED;
  +       vma->vm_flags |= VM_HUGETLB | VM_DONTEXPAND | VM_DONTDUMP;
          vma->vm_ops = &hugetlb_vm_ops;
   
          if (vma->vm_pgoff & (~huge_page_mask(h) >> PAGE_SHIFT))

I think we don't have to set VM_DONTDUMP on hugetlbfs's vma.

Thanks,
Naoya
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