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Re: [Xen-devel] [PATCH RESEND] xen/gntdev: Grant maps should not be subject to NUMA balancing

From Olaf Hering <olaf@aepfle.de>
Newsgroups linux.kernel
Subject Re: [Xen-devel] [PATCH RESEND] xen/gntdev: Grant maps should not be subject to NUMA balancing
Date 2016-11-10 17:30 +0100
Message-ID <sC0oF-as-17@gated-at.bofh.it> (permalink)
References <qtnoS-1h5-21@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Tue, Nov 10, Boris Ostrovsky wrote:

> Doing so will cause the grant to be unmapped and then, during
> fault handling, the fault to be mistakenly treated as NUMA hint
> fault.
> 
> In addition, even if those maps could partcipate in NUMA
> balancing, it wouldn't provide any benefit since we are unable
> to determine physical page's node (even if/when VNUMA is
> implemented).
> 
> Marking grant maps' VMAs as VM_IO will exclude them from being
> part of NUMA balancing.

This breaks qdisk+aio because now such pages are rejected with -EFAULT:

check_vma_flags
__get_user_pages
__get_user_pages_locked
__get_user_pages_unlocked
get_user_pages_fast
iov_iter_get_pages
dio_refill_pages
do_direct_IO
do_blockdev_direct_IO
do_blockdev_direct_IO
ext4_direct_IO_read
generic_file_read_iter
aio_run_iocb

domU.cfg:
builder=hvm
disk=['vdev=xvda, direct-io-safe, backendtype=qdisk, target=img.raw']

> @@ -802,7 +802,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
> -	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
> +	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_IO;


Olaf

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Re: [Xen-devel] [PATCH RESEND] xen/gntdev: Grant maps should not be  subject to NUMA balancing Olaf Hering <olaf@aepfle.de> - 2016-11-10 17:30 +0100
  Re: [Xen-devel] [PATCH RESEND] xen/gntdev: Grant maps should not be  subject to NUMA balancing Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-11-10 17:40 +0100
    Re: [Xen-devel] [PATCH RESEND] xen/gntdev: Grant maps should not be  subject to NUMA balancing Olaf Hering <olaf@aepfle.de> - 2016-11-10 17:50 +0100
      Re: [Xen-devel] [PATCH RESEND] xen/gntdev: Grant maps should not be  subject to NUMA balancing Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-11-10 18:40 +0100
        Re: [Xen-devel] [PATCH RESEND] xen/gntdev: Grant maps should not be  subject to NUMA balancing Olaf Hering <olaf@aepfle.de> - 2016-11-10 18:50 +0100
          Re: [Xen-devel] [PATCH RESEND] xen/gntdev: Grant maps should not be  subject to NUMA balancing David Vrabel <david.vrabel@citrix.com> - 2016-11-10 18:50 +0100
            Re: [Xen-devel] [PATCH RESEND] xen/gntdev: Grant maps should not be  subject to NUMA balancing Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-11-10 19:10 +0100

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