netdev - Re: [PATCH] tcp_mem initialization

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Message-ID: <45F992E1.1060604@psc.edu>
Date:	Thu, 15 Mar 2007 14:39:29 -0400
From:	John Heffner <jheffner@....edu>
To:	David Miller <davem@...emloft.net>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH] tcp_mem initialization

David Miller wrote:
> From: John Heffner <jheffner@....edu>
> Date: Wed, 14 Mar 2007 17:25:22 -0400
> 
>> The current tcp_mem initialization gives values that are really too 
>> small for systems with ~256-768 MB of memory, and also for systems with 
>> larger page sizes (ia64).  This patch gives an alternate method of 
>> initialization that doesn't depend on the cache allocation functions, 
>> but I think should still provide a nice curve that gives a smaller 
>> fraction of total memory with small-memory systems, while maintaining 
>> the same upper bound (pressure at 1/2, max as 3/4) on larger memory systems.
> 
> Indeed, it's really dumb for any of these calculations to be
> dependant upon the page size.
> 
> Your patch looks good, and I'll review it further tomorrow and
> push upstream unless I find some issues with it.
> 
> Thanks John.


The way it's coded is somewhat opaque since it has to be done with 
32-bit integer arithmetic.  These plots might help make the motivation 
behind the code a little clearer.

Thanks,
   -John

Download attachment "tcp_mem_pressure.png" of type "image/png" (9994 bytes)

Download attachment "tcp_mem_frac.png" of type "image/png" (10756 bytes)