netdev - Re: [PATCH] xen/netfront: improve truesize tracking

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Message-ID: <1356017968.21834.2859.camel@edumazet-glaptop>
Date:	Thu, 20 Dec 2012 07:39:28 -0800
From:	Eric Dumazet <erdnetdev@...il.com>
To:	Sander Eikelenboom <linux@...elenboom.it>
Cc:	Ian Campbell <Ian.Campbell@...rix.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	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 Thu, 2012-12-20 at 13:51 +0100, Sander Eikelenboom wrote:

> Eric:
>      From the warn_on_once, delta should be smaller than len, but probably they should be as close together as possible.
>      When you say "accurate estimation", what would be a acceptable difference between DELTA and LEN ?

I would use the most exact value, which is :

   skb->truesize += nr_frags * PAGE_SIZE;

Then, if we can spot later a regression in some stacks, adapt the
limiting parameters. I did a lot of work in GRO and TCP stack to reduce
the memory, and further changes are possible.

We really want to account memory, because we want to control how memory
is used on our machines and don't let some users use more than the
amount that was allowed to them.



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