netdev - Re: [RFC 0/2] vduse: add support for networking devices

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Message-ID: <ZEGG2GJw2DQk689j@x1n>
Date:   Thu, 20 Apr 2023 14:39:20 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Maxime Coquelin <maxime.coquelin@...hat.com>,
        xieyongji@...edance.com, mst@...hat.com, david.marchand@...hat.com,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        xuanzhuo@...ux.alibaba.com, eperezma@...hat.com
Subject: Re: [RFC 0/2] vduse: add support for networking devices

On Thu, Apr 20, 2023 at 12:34:06PM +0800, Jason Wang wrote:
> > 3. Coredump:
> >   In order to be able to perform post-mortem analysis, DPDK
> >   Vhost library marks pages used for vrings and descriptors
> >   buffers as MADV_DODUMP using madvise(). However with
> >   VDUSE it fails with -EINVAL. My understanding is that we
> >   set VM_DONTEXPAND flag to the VMAs and madvise's
> >   MADV_DODUMP fails if it is present. I'm not sure to
> >   understand why madvise would prevent MADV_DODUMP if
> >   VM_DONTEXPAND is set. Any thoughts?
> 
> Adding Peter who may know the answer.

I don't.. but I had a quick look, it seems that VM_DONTEXPAND was kind of
reused (and I'm not sure whether it's an abuse or not so far..) to
represent device driver pages since removal of VM_RESERVED:

https://lore.kernel.org/all/20120731103457.20182.88454.stgit@zurg/
https://lore.kernel.org/all/20120731103503.20182.94365.stgit@zurg/

But I think that change at least breaks hugetlb once so there's the
explicit hugetlb check to recover that behavior back:

https://lore.kernel.org/all/20180930054629.29150-1-daniel@linux.ibm.com/

Thanks,

-- 
Peter Xu