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Date:   Mon, 2 Jul 2018 15:37:33 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Laurent Dufour <ldufour@linux.vnet.ibm.com>
Cc:     Yang Shi <yang.shi@linux.alibaba.com>, willy@infradead.org,
        akpm@linux-foundation.org, peterz@infradead.org, mingo@redhat.com,
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        hpa@zytor.com, linux-mm@kvack.org, x86@kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC v3 PATCH 5/5] x86: check VM_DEAD flag in page fault
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On Mon 02-07-18 15:33:11, Laurent Dufour wrote:
> 
> 
> On 02/07/2018 14:45, Michal Hocko wrote:
> > On Mon 02-07-18 14:26:09, Laurent Dufour wrote:
> >> On 02/07/2018 14:15, Michal Hocko wrote:
[...]
> >>> We already do have a model for that. Have a look at MMF_UNSTABLE.
> >>
> >> MMF_UNSTABLE is a mm's flag, here this is a VMA's flag which is checked.
> > 
> > Yeah, and we have the VMA ready for all places where we do check the
> > flag. check_stable_address_space can be made to get vma rather than mm.
> 
> Yeah, this would have been more efficient to check that flag at the beginning
> of the page fault handler rather than the end, but this way it will be easier
> to handle the speculative page fault too ;)

The thing is that it doesn't really need to be called earlier. You are
not risking data corruption on file backed mappings.

-- 
Michal Hocko
SUSE Labs