netdev - Re: [RFC/PATCH 0/3] UDP memory usage accounting

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Message-ID: <4700FC74.6000601@hitachi.com>
Date:	Mon, 01 Oct 2007 22:56:04 +0900
From:	Satoshi OSHIMA <satoshi.oshima.fk@...achi.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	David Miller <davem@...emloft.net>, johnpol@....mipt.ru,
	netdev@...r.kernel.org, haoki@...hat.com, yoshfuji@...ux-ipv6.org,
	yumiko.sugita.yf@...achi.com,
	Evgeniy Polyakov <johnpol@....mipt.ru>
Subject: Re: [RFC/PATCH 0/3] UDP memory usage accounting

Herbert Xu wrote:
> On Fri, Sep 28, 2007 at 09:51:59PM -0700, David Miller wrote:
>> There is a per-socket send buffer limit, and there is a per-user open
>> file descriptor limit.  Multiply the two to determine how much system
>> memory the user can consume using sockets.
>
> We do have these limits but they're per-process, not per-user.
> Unless you lock down the number of processes each user can have
> to no more than a handful then this is basically useless.
>
> For example, let's say each socket can lock down 64K of kernel
> memory (which is quite easy to do BTW, just open a TCP/UDP socket,
> send data to it from another socket but keep the data in the
> socket by not calling recvmsg), and that each process can have
> 1024 file descriptors (the default), then each process can pin
>
> 64K x 1024 = 64M
>
> of memory.  So if the user can have 10 processes, then that's
> 640M of kernel memory that can be pinned down.  Usually the
> process limit is at least 10 times higher.

Thank you very mush for your comment.

What you pointed out is my motivation to make this patch.
I think that per-process limits won't help to solve this
problem.
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