linux-kernel - Re: LTP regressions due to 6dc296e7df4c ("mm: make sure all file VMAs have ->vm

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Date:	Mon, 14 Sep 2015 21:20:33 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Will Deacon <will.deacon@....com>, hpa@...or.com,
	luto@...capital.net, dave.hansen@...ux.intel.com, mingo@...e.hu,
	minchan@...nel.org, tglx@...utronix.de, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: LTP regressions due to 6dc296e7df4c ("mm: make sure all file
 VMAs have ->vm_ops set")

On Mon, Sep 14, 2015 at 07:05:47PM +0200, 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;

No. This would give a lot false positives from drives which setup page
tables upfront and don't use ->fault at all.

> 	 }
> 
> and remove the "vma->vm_file && !vma->vm_ops" checks in mmap_region() paths.
> 
> I dunno.
> 
> Oleg.
> 
> --
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-- 
 Kirill A. Shutemov
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