linux-kernel - Re: [PATCH] net: add per device sg_max

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Message-ID: <CANn89iLabW-Bz7DuECB8PjtbzqYPhxKmYSO3Mj5yPy2-046h5A@mail.gmail.com>
Date:	Wed, 13 Jan 2016 07:44:26 -0800
From:	Eric Dumazet <edumazet@...gle.com>
To:	David Miller <davem@...emloft.net>
Cc:	Hans Westgaard Ry <hans.westgaard.ry@...cle.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	David Laight <David.Laight@...lab.com>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Jiri Pirko <jiri@...lanox.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Salam Noureddine <noureddine@...sta.com>,
	Jarod Wilson <jarod@...hat.com>,
	Toshiaki Makita <makita.toshiaki@....ntt.co.jp>,
	Julian Anastasov <ja@....bg>,
	Ying Xue <ying.xue@...driver.com>,
	Craig Gallek <kraig@...gle.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Edward Jee <edjee@...gle.com>,
	Julia Lawall <julia.lawall@...6.fr>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Haakon Bugge <haakon.bugge@...cle.com>,
	Knut Omang <knut.omang@...cle.com>,
	Wei Lin Guay <wei.lin.guay@...cle.com>,
	Santosh Shilimkar <santosh.shilimkar@...cle.com>,
	Yuval Shaia <yuval.shaia@...cle.com>
Subject: Re: [PATCH] net: add per device sg_max_frags for skb

On Wed, Jan 13, 2016 at 7:38 AM, David Miller <davem@...emloft.net> wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> Date: Wed, 13 Jan 2016 06:19:11 -0800
>
>> 2) TCP stack has coalescing support. write(2) or sendmsg(2) should
>> append data into the last skb in write queue, and still use 32 KB
>> frags.
>
> Another way to get pathological SKBs is to do lots of tiny sendpage()
> calls over discontiguous areas of the file.

Yes, this was what I mentioned in the following sentence.
"You get pathological skb when using sendpage() or ..."