linux-kernel - Re: mmap vs. real memory

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Message-ID: <4AA988B2.4060102@nortel.com>
Date:	Thu, 10 Sep 2009 17:16:02 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	Brian McGrew <brian@...ionpro.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: mmap vs. real memory

On 09/10/2009 04:38 PM, Brian McGrew wrote:

> Now that we are needing more and more shared memory, we're seeing random
> performance issues.  With 16MB, 64MB and 256MB (in recent past) all was
> good.  But now, trying to allocate 1GB of shared memory, we see it taking
> anywhere from .6 to 9 SEONDS to access the file.  No good!
> 
> What I'm wondering and needed to do is map a chunk of mymoery (1GB today,
> maybe 2GB later on) so that all my apps can access it.  Short of creating a
> ramdisk and moving the mmap'ed file to ramdisk, what is the best way to do
> this???

Maybe make a ramfs partition, mount it somewhere, and create your file
there?  This is more efficient and simpler than creating a ramdisk.

Alternately, have you considered using hugetlbfs and mapping the shared
memory with large pages?

Chris
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