netdev - Re: network namespace bloat

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Date:	Thu, 19 Feb 2015 14:49:29 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	ebiederm@...ssion.com
Cc:	edumazet@...gle.com, netdev@...r.kernel.org,
	stephen@...workplumber.org, nicolas.dichtel@...nd.com,
	roopa@...ulusnetworks.com, hannes@...essinduktion.org,
	ddutt@...ulusnetworks.com, vipin@...ulusnetworks.com,
	shmulik.ladkani@...il.com, dsahern@...il.com
Subject: Re: network namespace bloat

From: ebiederm@...ssion.com (Eric W. Biederman)
Date: Tue, 10 Feb 2015 21:18:13 -0600

> Eric Dumazet <edumazet@...gle.com> writes:
> 
>> On Tue, Feb 10, 2015 at 6:42 PM, Eric W. Biederman
>> <ebiederm@...ssion.com> wrote:
>>
>>>
>>> Those large hash tables impact creation speed as large memory
>>> allocations require more work from the memory allocators, and they
>>> affect reliability of as order > 0 pages are not reliabily available in
>>> the kernel.  So from a network namespace perspective I would really like
>>> to convert the per network namespace hash tables to hash tables that
>>> have a single instance across all network namespaces.
>>>
>>
>> tcp_metric can fallback to vzalloc() after commit 976a702ac9eea ?
> 
> True, although vmalloc space is limited on some architectures.
> 
>> There is nothing preventing to use a single tcp_metric, a bit like
>> global TCP hash table.
>>
>> We only have to convert the thing...
> 
> Thanks for the confirmation, that is what I figured was going on.
> 
>> Note : At Google we do not save tcp metrics.
>> We have to use it only for FastOpen cookies eventually (For clients)
> 
> Interesting.  That makes it doubly desirable to not need to allocate
> a per network namespace hash table.

As a first step we can make the tcp_metrics hash global, but in addition
to that an rhashtable conversion is probably in order as well.
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