From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <38209F51.CCADD7D0@kscable.com> Date: Wed, 03 Nov 1999 14:47:13 -0600 From: Tom Hull Reply-To: thull@kscable.com MIME-Version: 1.0 Subject: Re: The 64GB memory thing References: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Ingo Molnar Cc: Linux MM List-ID: Ingo Molnar wrote: > > On Wed, 3 Nov 1999, Neil Conway wrote: > > > And presumably each process is still limited to a 32-bit address space, > > right? > > yes, this is a fundamental limitation of x86 processors. Under Linux -in > all 3 high memory modes- user-space virtual memory is 3GB. Nevertheless on > a 8-way box you likely want to run either lots of processes, or a few (but > more than 8 ) processes/threads to use up all available CPU time. This > means with 8x 2GB RSS number crunching processes we already cover 16GB > RAM. So it's not at all unrealistic to have support for more than 4GB RAM! > The foundation for this is that under Linux all 64GB RAM can be mapped > into user processes transparently. I believe other x86 unices (not to talk > about NT) do not have this propertly, they handle 'high memory' as a > special kind of RAM which can be accessed through special system calls. SCO UnixWare (as of Release 7.1) has the ability to transparently map PAE-addressable memory into user processes. A brief history: Starting with 7.0 (Spring 1998), SCO UnixWare supports PAE mode for accessing physical memory up to 64GB. In 7.0, such memory (called Dedicated Memory) was only available for shared memory segments. New system calls (called dshm) were introduced at that time. The dshm calls are not necessary for a user process to access high (above 4GB) memory, but without dshm a user process is limited to its 3GB virtual address space. Dshm provides a window for dynamically mapping a portion of a much larger shared memory segment into the user's ddress space. UnixWare 7.1 (Spring 1999) support for using high memory for all purposes. The default tuning limits general purpose memory to 8GB, and retains the concept of Dedicated Memory for memory above the general purpose memory tune point. The tuning can be adjusted by changing a boot parameter, so that general purpose memory size can be increased to larger values if the workload permits. (The example of 8x 2GB RSS number crunchine process is a relatively painless scenario.) -- /* * Tom Hull -- mailto:thull@kscable.com or thull@ocston.org * http://www.ocston.org/~thull/ */ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://humbolt.geo.uu.nl/Linux-MM/