More then 2G of memory per process

jstoltz jstoltz at
Thu Aug 7 09:47:00 CDT 2003

I got more info from our developers. The problem we are having is the
current limitation is 1gig in heap and 2gig in shared memory. Unfortunately,
exceeding one of these is enough to start failing allocation, so we've seen
ourselves go down around 1.8 gig allocated. (Exceeded the 1gig heap limit at
this threshold, so the fact that more shared was theoretically available
didn't help.)

Will the 4G/4G patch be useful in this situation?


-----Original Message-----
From: Matt Domsch [mailto:Matt_Domsch at] 
Sent: Tuesday, August 05, 2003 2:33 PM
To: Jeremy Stoltz
Cc: linux-poweredge at
Subject: Re: More then 2G of memory per process

> I'm running an application that was developed in house. We are 
> starting to exceed the limit of approximately 2 gigs of memory per 
> application. Are there any options that will allow us to increase this 
> limit?

Red Hat Enterprise Linux 3 public beta "Taroon" has a 'bigmem' kernel 
which implements a 4GB kernel / 4GB user memory split.  This increases the 
amount of address space available to user processes from 3GB to just under 
4GB, which should help a good bit.  It *really* helps the kernel, as it 
now gets 4GB of address space, up from 1GB previously.

There is a performance penalty to switching to a 4GB/4GB model from the 
current 1GB/3GB model in use today.  Each application will behave 
somewhate differently.  We'd love to hear what your performance 
differences are between running on a kernel with a 3/1 split vs. a 4/4 

> We are currently using 7.3 bigmem kernel with 4 gigs of physical ram. 
> I'm planning on increasing the physical ram to 8 gigs.

There are no plans to release a 4/4 split kernel for products such as 


Matt Domsch
Sr. Software Engineer, Lead Engineer
Dell Linux Solutions
Linux on Dell mailing lists @

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