netdev - Re: [PATCH net-next] myri10ge: fix truesize underestimation

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Message-ID: <1319144356.2854.36.camel@edumazet-laptop>
Date:	Thu, 20 Oct 2011 22:59:16 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Andrew Gallatin <gallatin@...i.com>
Cc:	Jon Mason <mason@...i.com>, David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] myri10ge: fix truesize underestimation

Le jeudi 20 octobre 2011 à 16:45 -0400, Andrew Gallatin a écrit :
> On 10/20/11 16:44, Eric Dumazet wrote:
> > Le jeudi 20 octobre 2011 à 15:33 -0500, Jon Mason a écrit :
> >> On Thu, Oct 20, 2011 at 3:10 PM, Eric Dumazet<eric.dumazet@...il.com>  wrote:
> >>> skb->truesize must account for allocated memory, not the used part of
> >>> it. Doing this work is important to avoid unexpected OOM situations.
> >>>
> >>> Signed-off-by: Eric Dumazet<eric.dumazet@...il.com>
> >>
> >> Acked-by: Jon Mason<mason@...i.com>
> >
> > Thanks for reviewing Jon !
> >
> >
> 
> Please wait a second..  I think the patch is incorrect.
> 
> There is already code in myri10ge_rx_skb_build() which
> attempts to set the truesize.  However, it sets it to
> the used, rather than the allocated size so it is apparently
> incorrect.
> 
> I'd prefer we fix that code.

Well, I believe I did exactly that :)

truesize of initial skb is fine.

Then for everay frag added, you must add to skb-truesize the allocated
memory for this frag.

You add frags of a given size (small or big)

In the end, its truesize += bytes * number_of_frags

(bytes being small_size or big_size)


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