Re: [RFC PATCH 0/7] dax, ext4: Synchronous page faults

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On Sun, Aug 13, 2017 at 2:25 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> On Sat, Aug 12, 2017 at 07:44:14PM -0700, Dan Williams wrote:
>> How about MAP_SYNC == (MAP_SHARED|MAP_PRIVATE)? On older kernels that
>> should get -EINVAL, and on new kernels it means SYNC+SHARED.
>
> Cute trick, but I'd hate to waster it just for our little flag.
>
> How about:
>
> #define __MAP_VALIDATE          MAP_SHARED|MAP_PRIVATE
> #define MAP_SYNC                0x??? | __MAP_VALIDATE
>
> so that we can reuse that trick for any new flag?

Yes, even better. I think that effectively kicks the need for mmap3()
down the road a bit.



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