netdev - Re: [PATCH net-next v1] xsk: support use vaddr as ring

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Message-ID: <CAJ8uoz0EqC81hJRw=3dj6vE99Y6+Y6daN3ugrSWhAUzrgYUT1Q@mail.gmail.com>
Date:   Fri, 10 Feb 2023 10:52:20 +0100
From:   Magnus Karlsson <magnus.karlsson@...il.com>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc:     netdev@...r.kernel.org,
        Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>, bpf@...r.kernel.org,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH net-next v1] xsk: support use vaddr as ring

On Fri, 10 Feb 2023 at 03:14, Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> When we try to start AF_XDP on some machines with long running time, due
> to the machine's memory fragmentation problem, there is no sufficient
> continuous physical memory that will cause the start failure.
>
> After AF_XDP fails to apply for continuous physical memory, this patch
> tries to use vmalloc() to allocate memory to solve this problem.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> Reported-by: kernel test robot <lkp@...el.com>
> Link: https://lore.kernel.org/oe-kbuild-all/202302091850.0HBmsDAq-lkp@intel.com
> ---
>  net/xdp/xsk.c       |  8 +++++---
>  net/xdp/xsk_queue.c | 21 +++++++++++++++------
>  net/xdp/xsk_queue.h |  1 +
>  3 files changed, 21 insertions(+), 9 deletions(-)
>
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index 9f0561b67c12..33db57548ee3 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -1296,7 +1296,6 @@ static int xsk_mmap(struct file *file, struct socket *sock,
>         struct xdp_sock *xs = xdp_sk(sock->sk);
>         struct xsk_queue *q = NULL;
>         unsigned long pfn;
> -       struct page *qpg;
>
>         if (READ_ONCE(xs->state) != XSK_READY)
>                 return -EBUSY;
> @@ -1319,10 +1318,13 @@ static int xsk_mmap(struct file *file, struct socket *sock,
>
>         /* Matches the smp_wmb() in xsk_init_queue */
>         smp_rmb();
> -       qpg = virt_to_head_page(q->ring);
> -       if (size > page_size(qpg))
> +
> +       if (PAGE_ALIGN(q->ring_size) < size)
>                 return -EINVAL;
>
> +       if (is_vmalloc_addr(q->ring))
> +               return remap_vmalloc_range(vma, q->ring, 0);
> +
>         pfn = virt_to_phys(q->ring) >> PAGE_SHIFT;
>         return remap_pfn_range(vma, vma->vm_start, pfn,
>                                size, vma->vm_page_prot);
> diff --git a/net/xdp/xsk_queue.c b/net/xdp/xsk_queue.c
> index 6cf9586e5027..7b03102d1672 100644
> --- a/net/xdp/xsk_queue.c
> +++ b/net/xdp/xsk_queue.c
> @@ -7,6 +7,7 @@
>  #include <linux/slab.h>
>  #include <linux/overflow.h>
>  #include <net/xdp_sock_drv.h>
> +#include <linux/vmalloc.h>
>
>  #include "xsk_queue.h"
>
> @@ -37,14 +38,18 @@ struct xsk_queue *xskq_create(u32 nentries, bool umem_queue)
>                     __GFP_COMP  | __GFP_NORETRY;
>         size = xskq_get_ring_size(q, umem_queue);
>
> +       q->ring_size = size;
>         q->ring = (struct xdp_ring *)__get_free_pages(gfp_flags,
>                                                       get_order(size));
> -       if (!q->ring) {
> -               kfree(q);
> -               return NULL;
> -       }
> +       if (q->ring)
> +               return q;
> +
> +       q->ring = (struct xdp_ring *)vmalloc_user(size);
> +       if (q->ring)
> +               return q;

Thanks for bringing this to attention. Interesting to see how hard it
gets after a while to find consecutive memory since this is not a
large area.

I am wondering if it would be better to remove the __get_free_pages()
and just go for vmalloc_user. There is no particular reason here for
allocating consecutive physical pages for the ring. Does anyone see
any problem with removing this? If not, please just remove
__get_free_pages(), test it, and post a v2.

> -       return q;
> +       kfree(q);
> +       return NULL;
>  }
>
>  void xskq_destroy(struct xsk_queue *q)
> @@ -52,6 +57,10 @@ void xskq_destroy(struct xsk_queue *q)
>         if (!q)
>                 return;
>
> -       page_frag_free(q->ring);
> +       if (is_vmalloc_addr(q->ring))
> +               vfree(q->ring);
> +       else
> +               page_frag_free(q->ring);
> +
>         kfree(q);
>  }
> diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
> index c6fb6b763658..35922b8b92a8 100644
> --- a/net/xdp/xsk_queue.h
> +++ b/net/xdp/xsk_queue.h
> @@ -45,6 +45,7 @@ struct xsk_queue {
>         struct xdp_ring *ring;
>         u64 invalid_descs;
>         u64 queue_empty_descs;
> +       size_t ring_size;
>  };
>
>  /* The structure of the shared state of the rings are a simple
> --
> 2.32.0.3.g01195cf9f
>