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Date: Thu, 21 Aug 2014 17:46:01 -0400
From: Peter Feiner <pfeiner@google.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Pavel Emelyanov <xemul@parallels.com>,
        Jamie Liu <jamieliu@google.com>, Hugh Dickins <hughd@google.com>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Magnus Damm <damm@opensource.se>
Subject: Re: [PATCH] mm: softdirty: write protect PTEs created for read
 faults after VM_SOFTDIRTY cleared
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On Fri, Aug 22, 2014 at 12:39:42AM +0300, Kirill A. Shutemov wrote:
> On Fri, Aug 22, 2014 at 12:51:15AM +0400, Cyrill Gorcunov wrote:
> 
> Looks good to me.
> 
> Would you mind to apply the same pgprot_modify() approach on the
> clear_refs_write(), test and post the patch?
> 
> Feel free to use my singed-off-by (or suggested-by if you prefer) once
> it's tested (see merge case below).

Sure thing :-)

> One thing: there could be (I haven't checked) complications on
> vma_merge(): since vm_flags are identical it assumes that it can reuse
> vma->vm_page_prot of expanded vma. But VM_SOFTDIRTY is excluded from
> vm_flags compatibility check. What should we do with vm_page_prot there?

Since the merged VMA will have VM_SOFTDIRTY set, it's OK that it's vm_page_prot
won't be setup for write notifications. For the purpose of process migration,
you'll just get some false positives, which is tolerable.