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Date: Mon, 14 Sep 2015 19:46:09 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>, hpa@zytor.com, luto@amacapital.net,
        dave.hansen@linux.intel.com, mingo@elte.hu, minchan@kernel.org,
        tglx@linutronix.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: LTP regressions due to 6dc296e7df4c ("mm: make sure all file
	VMAs have ->vm_ops set")
Message-ID: <20150914174609.GA30917@redhat.com>
References: <20150914105346.GB23878@arm.com> <20150914115800.06242CE@black.fi.intel.com> <20150914170547.GA28535@redhat.com>
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On 09/14, Oleg Nesterov wrote:
>
> On 09/14, Kirill A. Shutemov wrote:
> >
> > Fix is below. I don't really like it, but I cannot find any better
> > solution.
>
> Me too...
>
> But this change "documents" the nasty special "vm_file && !vm_ops" case, and
> I am not sure how we can remove it later...
>
> So perhaps we should change vma_is_anonymous() back to check ->fault too,
>
> 	 static inline bool vma_is_anonymous(struct vm_area_struct *vma)
> 	 {
> 	-	return !vma->vm_ops;
> 	+	return !vma->vm_ops || !vma->vm_ops->fault;
> 	 }
>
> and remove the "vma->vm_file && !vma->vm_ops" checks in mmap_region() paths.
  ^^^

sorry, I actually meant "or remove". But perhaps "and" makes sense too.

Say, if we change vma_is_anonymous() as above, then we can kill
arch_vma_name() on x86. mpx_mmap() can install the dummy vm_ops with
the single ->name() method.

> I dunno.

Yes. Up to you.

Oleg.