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Message-ID: <42945636.VKLsUkgjGN@silver>
Date: Fri, 17 Sep 2021 14:02:04 +0200
From: Christian Schoenebeck <linux_oss@...debyte.com>
To: v9fs-developer@...ts.sourceforge.net
Cc: netdev@...r.kernel.org,
Dominique Martinet <asmadeus@...ewreck.org>,
Eric Van Hensbergen <ericvh@...il.com>,
Latchesar Ionkov <lucho@...kov.net>,
Greg Kurz <groug@...d.org>, Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH 6/7] 9p/trans_virtio: support larger msize values
On Donnerstag, 16. September 2021 20:25:16 CEST Christian Schoenebeck wrote:
> The virtio transport supports by default a 9p 'msize' of up to
> approximately 500 kB. This patches adds support for larger 'msize'
> values by resizing the amount of scatter/gather lists if required.
>
> Signed-off-by: Christian Schoenebeck <linux_oss@...debyte.com>
> ---
s/patches/patch/
> net/9p/trans_virtio.c | 52 +++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 52 insertions(+)
>
> diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
> index 1a45e0df2336..1f9a0283d7b8 100644
> --- a/net/9p/trans_virtio.c
> +++ b/net/9p/trans_virtio.c
> @@ -195,6 +195,30 @@ static struct virtqueue_sg *vq_sg_alloc(unsigned int
> nsgl) return vq_sg;
> }
>
> +/**
> + * Resize passed virtqueue scatter/gather lists to the passed amount of
> + * list blocks.
> + * @_vq_sg: scatter/gather lists to be resized
> + * @nsgl: new amount of scatter/gather list blocks
> + */
> +static int vq_sg_resize(struct virtqueue_sg **_vq_sg, unsigned int nsgl)
> +{
> + struct virtqueue_sg *vq_sg;
> +
> + BUG_ON(!_vq_sg || !nsgl);
> + vq_sg = *_vq_sg;
> + if (vq_sg->nsgl == nsgl)
> + return 0;
> +
> + /* lazy resize implementation for now */
> + vq_sg = vq_sg_alloc(nsgl);
> + if (!vq_sg)
> + return -ENOMEM;
> +
Missing
kfree(*_vq_sg);
here, and probably also a prior memcpy() as in patch 7, i.e.:
/* copy over old scatter gather lists */
sz = sizeof(struct virtqueue_sg) +
(*_vq_sg)->nsgl * sizeof(struct scatterlist *);
memcpy(vq_sg, *_vq_sg, sz);
> + *_vq_sg = vq_sg;
> + return 0;
> +}
> +
> /**
> * p9_virtio_close - reclaim resources of a channel
> * @client: client instance
> @@ -766,6 +790,10 @@ p9_virtio_create(struct p9_client *client, const char
> *devname, char *args) struct virtio_chan *chan;
> int ret = -ENOENT;
> int found = 0;
> +#if !defined(CONFIG_ARCH_NO_SG_CHAIN)
> + size_t npages;
> + size_t nsgl;
> +#endif
>
> if (devname == NULL)
> return -EINVAL;
> @@ -788,6 +816,30 @@ p9_virtio_create(struct p9_client *client, const char
> *devname, char *args) return ret;
> }
>
> + /*
> + * if user supplied an 'msize' option that's larger than what this
> + * transport supports by default, then try to allocate more sg lists
> + */
> + if (client->msize > client->trans_maxsize) {
> +#if !defined(CONFIG_ARCH_NO_SG_CHAIN)
> + npages = DIV_ROUND_UP(client->msize, PAGE_SIZE);
> + if (npages > chan->p9_max_pages)
> + npages = chan->p9_max_pages;
> + nsgl = DIV_ROUND_UP(npages, SG_USER_PAGES_PER_LIST);
> + if (nsgl > chan->vq_sg->nsgl) {
> + /*
> + * if resize fails, no big deal, then just
> + * continue with default msize instead
> + */
> + if (!vq_sg_resize(&chan->vq_sg, nsgl)) {
> + client->trans_maxsize =
> + PAGE_SIZE *
> + ((nsgl * SG_USER_PAGES_PER_LIST) - 3);
> + }
> + }
> +#endif /* !defined(CONFIG_ARCH_NO_SG_CHAIN) */
> + }
Probably an error/info message for architectures not supporting SG chains
would be useful here, to let users on those system know why they cannot get
beyond 500k msize.
> +
> client->trans = (void *)chan;
> client->status = Connected;
> chan->client = client;
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