linux-kernel - Re: [PATCH net v6 4/4] tg3: Fix tx_pending checks for tg3_tso

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Message-ID: <1409961810.26422.149.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 05 Sep 2014 17:03:30 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Prashant Sreedharan <prashant@...adcom.com>
Cc:	Benjamin Poirier <bpoirier@...e.de>,
	Michael Chan <mchan@...adcom.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v6 4/4] tg3: Fix tx_pending checks for tg3_tso_bug

On Fri, 2014-09-05 at 16:35 -0700, Prashant Sreedharan wrote:

> fyi.. Initially the driver was doing a skb_copy()
> (tigon3_dma_hwbug_workaround()) for LSO skb that met HW bug conditions
> but users started reporting page allocation failures due to copying of
> large LSO skbs. To avoid this Commit 4caab52eb102f1 (tg3: Prevent page
> allocation failure during TSO workaround) changed the driver logic to do
> skb_gso_segment() for LSO skbs that met the HW bug conditions. With
> skb_linearize() we might end up again with memory allocation failures
> for large LSO skbs though at a much less frequent level (ie when TX
> queue is almost full). 

Note that TCP stack has one skb collapse feature, currently limited in
allocation of linear skbs fitting a whole page.

Instead of this private helper (and pretty limited one btw), we could
add a core function, that would build skbs with order-0 fragments.

Instead of skb_linearize(), I guess many call sites could instead use
this new helper.

Because as you said, skb_linearize() of one 64KB GSO packet can ask
order-5 allocations, and this generally does not work reliably.


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