From: Stefan Hajnoczi <stefanha@redhat.com>
To: Connor Kuehl <ckuehl@redhat.com>
Cc: virtio-fs@redhat.com, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org, vgoyal@redhat.com,
miklos@szeredi.hu, jasowang@redhat.com, mst@redhat.com
Subject: Re: [PATCH 2/3] virtiofs: split requests that exceed virtqueue size
Date: Mon, 22 Mar 2021 15:47:37 +0000 [thread overview]
Message-ID: <YFi8GYrRG/ks2BBz@stefanha-x1.localdomain> (raw)
In-Reply-To: <20210318135223.1342795-3-ckuehl@redhat.com>
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On Thu, Mar 18, 2021 at 08:52:22AM -0500, Connor Kuehl wrote:
> If an incoming FUSE request can't fit on the virtqueue, the request is
> placed onto a workqueue so a worker can try to resubmit it later where
> there will (hopefully) be space for it next time.
>
> This is fine for requests that aren't larger than a virtqueue's maximum
> capacity. However, if a request's size exceeds the maximum capacity of
> the virtqueue (even if the virtqueue is empty), it will be doomed to a
> life of being placed on the workqueue, removed, discovered it won't fit,
> and placed on the workqueue yet again.
>
> Furthermore, from section 2.6.5.3.1 (Driver Requirements: Indirect
> Descriptors) of the virtio spec:
>
> "A driver MUST NOT create a descriptor chain longer than the Queue
> Size of the device."
>
> To fix this, limit the number of pages FUSE will use for an overall
> request. This way, each request can realistically fit on the virtqueue
> when it is decomposed into a scattergather list and avoid violating
> section 2.6.5.3.1 of the virtio spec.
>
> Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
> ---
> fs/fuse/fuse_i.h | 5 +++++
> fs/fuse/inode.c | 7 +++++++
> fs/fuse/virtio_fs.c | 14 ++++++++++++++
> 3 files changed, 26 insertions(+)
Nice that FUSE already has max_pages :-).
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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next prev parent reply other threads:[~2021-03-22 15:49 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-18 13:52 [PATCH 0/3] virtiofs: split requests that exceed virtqueue size Connor Kuehl
2021-03-18 13:52 ` [PATCH 1/3] virtio_ring: always warn when descriptor chain exceeds queue size Connor Kuehl
2021-03-22 3:22 ` Jason Wang
2021-03-22 8:17 ` Michael S. Tsirkin
2021-03-23 2:38 ` Jason Wang
2021-03-18 13:52 ` [PATCH 2/3] virtiofs: split requests that exceed virtqueue size Connor Kuehl
2021-03-18 15:17 ` Miklos Szeredi
2021-03-18 15:52 ` Connor Kuehl
2021-03-20 20:04 ` Michael S. Tsirkin
2021-03-22 19:01 ` Vivek Goyal
2021-03-24 15:09 ` Connor Kuehl
2021-03-24 15:30 ` Miklos Szeredi
2021-03-24 15:31 ` Connor Kuehl
2021-03-19 13:49 ` Vivek Goyal
2021-03-19 14:16 ` Connor Kuehl
2021-03-22 15:47 ` Stefan Hajnoczi [this message]
2021-03-18 13:52 ` [PATCH 3/3] fuse: fix typo for fuse_conn.max_pages comment Connor Kuehl
2021-03-22 3:42 ` Jason Wang
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