linux-kernel - Re: [PATCH bpf-next 2/3] xdp: xdp_umem: replace kmap on vmap for umem map

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Message-ID: <9F98648A-8654-4767-97B5-CF4BC939393C@flugsvamp.com>
Date:   Tue, 13 Aug 2019 10:42:18 -0700
From:   "Jonathan Lemon" <jlemon@...gsvamp.com>
To:     "Ivan Khoronzhuk" <ivan.khoronzhuk@...aro.org>
Cc:     magnus.karlsson@...el.com, bjorn.topel@...el.com,
        davem@...emloft.net, hawk@...nel.org, john.fastabend@...il.com,
        jakub.kicinski@...ronome.com, daniel@...earbox.net,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        xdp-newbies@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 2/3] xdp: xdp_umem: replace kmap on vmap for umem
 map



On 13 Aug 2019, at 3:23, Ivan Khoronzhuk wrote:

> For 64-bit there is no reason to use vmap/vunmap, so use page_address
> as it was initially. For 32 bits, in some apps, like in samples
> xdpsock_user.c when number of pgs in use is quite big, the kmap
> memory can be not enough, despite on this, kmap looks like is
> deprecated in such cases as it can block and should be used rather
> for dynamic mm.
>
> Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>

Seems a bit overkill - if not high memory, kmap() falls back
to just page_address(), unlike vmap().
-- 
Jonathan

> ---
>  net/xdp/xdp_umem.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
> index a0607969f8c0..907c9019fe21 100644
> --- a/net/xdp/xdp_umem.c
> +++ b/net/xdp/xdp_umem.c
> @@ -14,7 +14,7 @@
>  #include <linux/netdevice.h>
>  #include <linux/rtnetlink.h>
>  #include <linux/idr.h>
> -#include <linux/highmem.h>
> +#include <linux/vmalloc.h>
>
>  #include "xdp_umem.h"
>  #include "xsk_queue.h"
> @@ -167,10 +167,12 @@ void xdp_umem_clear_dev(struct xdp_umem *umem)
>
>  static void xdp_umem_unmap_pages(struct xdp_umem *umem)
>  {
> +#if BITS_PER_LONG == 32
>  	unsigned int i;
>
>  	for (i = 0; i < umem->npgs; i++)
> -		kunmap(umem->pgs[i]);
> +		vunmap(umem->pages[i].addr);
> +#endif
>  }
>
>  static void xdp_umem_unpin_pages(struct xdp_umem *umem)
> @@ -378,8 +380,14 @@ static int xdp_umem_reg(struct xdp_umem *umem, 
> struct xdp_umem_reg *mr)
>  		goto out_account;
>  	}
>
> -	for (i = 0; i < umem->npgs; i++)
> -		umem->pages[i].addr = kmap(umem->pgs[i]);
> +	for (i = 0; i < umem->npgs; i++) {
> +#if BITS_PER_LONG == 32
> +		umem->pages[i].addr = vmap(&umem->pgs[i], 1, VM_MAP,
> +					   PAGE_KERNEL);
> +#else
> +		umem->pages[i].addr = page_address(umem->pgs[i]);
> +#endif
> +	}
>
>  	return 0;
>
> -- 
> 2.17.1