linux-kernel - Re: [PATCH v2] net:Add sysctl_tcp_sg_max_skb

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Message-ID: <1453907702.20722.6.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 27 Jan 2016 07:15:02 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hans Westgaard Ry <hans.westgaard.ry@...cle.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	"\"\"hannes@...essinduktion.org\"\"" <hannes@...essinduktion.org>,
	"open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>,
	Haakon Bugge <haakon.bugge@...cle.com>
Subject: Re: [PATCH v2] net:Add sysctl_tcp_sg_max_skb_frags

On Wed, 2016-01-27 at 14:20 +0100, Hans Westgaard Ry wrote:
> Devices may have limits on the number of fragments in an skb they support.
> Current codebase uses a constant as maximum for number of fragments one
> skb can hold and use.
> When enabling scatter/gather and running traffic with many small messages
> the codebase uses the maximum number of fragments and may thereby violate
> the max for certain devices.
> The patch introduces a global variable as max number of fragments in
> scatter/gather.


Principle looks good, but we have to ask if other skb providers [1] will
add other sysctl, or if we could share a common one ?

If it is a common one, it should be /proc/sys/net/core/... instead
of /proc/sys/net/ipv4/tcp_....



Other providers include :

1) GRO stack
2) callers of sock_alloc_send_pskb(), alloc_skb_with_frags(),
sock_alloc_send_skb() ..

Thanks !