[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <1355844398.14620.254.camel@zakaz.uk.xensource.com>
Date: Tue, 18 Dec 2012 15:26:38 +0000
From: Ian Campbell <Ian.Campbell@...rix.com>
To: Eric Dumazet <erdnetdev@...il.com>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
Sander Eikelenboom <linux@...elenboom.it>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
annie li <annie.li@...cle.com>,
"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
Subject: Re: [PATCH] xen/netfront: improve truesize tracking
On Tue, 2012-12-18 at 15:12 +0000, Eric Dumazet wrote:
> On Tue, 2012-12-18 at 13:51 +0000, Ian Campbell wrote:
> > Using RX_COPY_THRESHOLD is incorrect if the SKB is actually smaller
> > than that. We have already accounted for this in
> > NETFRONT_SKB_CB(skb)->pull_to so use that instead.
> >
> > Fixes WARN_ON from skb_try_coalesce.
> >
> > Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
> > Cc: Sander Eikelenboom <linux@...elenboom.it>
> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > Cc: annie li <annie.li@...cle.com>
> > Cc: xen-devel@...ts.xensource.com
> > Cc: netdev@...r.kernel.org
> > Cc: stable@...nel.org # 3.7.x only
> > ---
> > drivers/net/xen-netfront.c | 15 +++++----------
> > 1 files changed, 5 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> > index caa0110..b06ef81 100644
> > --- a/drivers/net/xen-netfront.c
> > +++ b/drivers/net/xen-netfront.c
> > @@ -971,17 +971,12 @@ err:
> > * overheads. Here, we add the size of the data pulled
> > * in xennet_fill_frags().
> > *
> > - * We also adjust for any unused space in the main
> > - * data area by subtracting (RX_COPY_THRESHOLD -
> > - * len). This is especially important with drivers
> > - * which split incoming packets into header and data,
> > - * using only 66 bytes of the main data area (see the
> > - * e1000 driver for example.) On such systems,
> > - * without this last adjustement, our achievable
> > - * receive throughout using the standard receive
> > - * buffer size was cut by 25%(!!!).
> > + * We also adjust for the __pskb_pull_tail done in
> > + * handle_incoming_queue which pulls data from the
> > + * frags into the head area, which is already
> > + * accounted in RX_COPY_THRESHOLD.
> > */
> > - skb->truesize += skb->data_len - RX_COPY_THRESHOLD;
> > + skb->truesize += skb->data_len - NETFRONT_SKB_CB(skb)->pull_to;
> > skb->len += skb->data_len;
> >
> > if (rx->flags & XEN_NETRXF_csum_blank)
>
>
> But skb truesize is not what you think.
Indeed, it seems I was completely backwards about what it means!
> You must account the exact memory used by this skb, not only the used
> part of it.
>
> At the very minimum, it should be
>
> skb->truesize += skb->data_len;
>
> But it really should be the allocated size of the fragment.
>
> If its a page, then its a page, even if you use one single byte in it.
So actually we want += PAGE_SIZE * skb_shinfo(skb)->nr_frags ?
Sander, can you try that change?
Ian.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Powered by blists - more mailing lists