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Re: [PATCH v3 (re-send)] xen/gntdev: Use mempolicy instead of VM_IO flag to avoid NUMA balancing

From Hugh Dickins <hughd@google.com>
Newsgroups linux.kernel
Subject Re: [PATCH v3 (re-send)] xen/gntdev: Use mempolicy instead of VM_IO flag to avoid NUMA balancing
Date 2016-11-18 23:30 +0100
Message-ID <sEZPs-4LL-23@gated-at.bofh.it> (permalink)
References <sEBap-5nI-11@gated-at.bofh.it> <sEZmp-4h6-7@gated-at.bofh.it> <sEZFL-4Iz-11@gated-at.bofh.it>
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On Fri, 18 Nov 2016, Boris Ostrovsky wrote:
> On 11/18/2016 04:51 PM, Hugh Dickins wrote:
> > Hmm, sorry, but this seems overcomplicated to me: ingenious, but an
> > unusual use of the ->get_policy method, which is a little worrying,
> > since it has only been used for shmem (+ shm and kernfs) until now.
> >
> > Maybe I'm wrong, but wouldn't substituting VM_MIXEDMAP for VM_IO
> > solve the problem more simply?
> 
> It would indeed. I didn't want to use it because it has specific meaning
> ("Can contain "struct page" and pure PFN pages") and that didn't seem
> like the right flag to describe this vma.

It is okay if it contains 0 pure PFN pages; and no worse than VM_IO was.
A comment on why VM_MIXEDMAP is being used there would certainly be good.
But I do find its use preferable to enlisting an unusual ->get_policy.

Hugh

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Thread

[PATCH v3 (re-send)] xen/gntdev: Use mempolicy instead of VM_IO flag to avoid NUMA balancing Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-11-17 21:10 +0100
  Re: [PATCH v3 (re-send)] xen/gntdev: Use mempolicy instead of VM_IO  flag to avoid NUMA balancing Olaf Hering <olaf@aepfle.de> - 2016-11-18 09:10 +0100
  Re: [PATCH v3 (re-send)] xen/gntdev: Use mempolicy instead of VM_IO  flag to avoid NUMA balancing Hugh Dickins <hughd@google.com> - 2016-11-18 23:00 +0100
    Re: [PATCH v3 (re-send)] xen/gntdev: Use mempolicy instead of VM_IO  flag to avoid NUMA balancing Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-11-18 23:20 +0100
      Re: [PATCH v3 (re-send)] xen/gntdev: Use mempolicy instead of VM_IO  flag to avoid NUMA balancing Hugh Dickins <hughd@google.com> - 2016-11-18 23:30 +0100
        Re: [PATCH v3 (re-send)] xen/gntdev: Use mempolicy instead of VM_IO  flag to avoid NUMA balancing Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-11-18 23:50 +0100
          Re: [PATCH v3 (re-send)] xen/gntdev: Use mempolicy instead of VM_IO  flag to avoid NUMA balancing Hugh Dickins <hughd@google.com> - 2016-11-19 00:30 +0100

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