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Re: [PATCH v7 0/8] Request for inclusion: tcp memory buffers

From:  David Miller <davem-AT-davemloft.net>
To:  glommer-AT-parallels.com
Subject:  Re: [PATCH v7 0/8] Request for inclusion: tcp memory buffers
Date:  Thu, 13 Oct 2011 16:12:21 -0400 (EDT)
Message-ID:  <20111013.161221.1969725742975317077.davem@davemloft.net>
Cc:  linux-kernel-AT-vger.kernel.org, akpm-AT-linux-foundation.org, lizf-AT-cn.fujitsu.com, kamezawa.hiroyu-AT-jp.fujitsu.com, ebiederm-AT-xmission.com, paul-AT-paulmenage.org, gthelen-AT-google.com, netdev-AT-vger.kernel.org, linux-mm-AT-kvack.org, kirill-AT-shutemov.name, avagin-AT-parallels.com, devel-AT-openvz.org
Archive-link:  Article

From: Glauber Costa <glommer@parallels.com>
Date: Fri, 14 Oct 2011 00:05:58 +0400

> Also, I kind of dispute the affirmation that !cgroup will encompass
> the majority of users, since cgroups is being enabled by default by
> most vendors. All systemd based systems use it extensively, for
> instance.

I will definitely advise people against this, since the cost of having
this on by default is absolutely non-trivial.

People keep asking every few releases "where the heck has my performance
gone" and it's because of creeping features like this.  This socket
cgroup feature is a prime example of where that kind of stuff comes
from.

I really get irritated when people go "oh, it's just one indirect
function call" and "oh, it's just one more pointer in struct sock"

We work really hard to _remove_ elements from structures and make them
smaller, and to remove expensive operations from the fast paths.

It might take someone weeks if not months to find a way to make a
patch which compensates for the extra overhead your patches are adding.

And I don't think you fully appreciate that.

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