Re: [Linux-ia64] Kernel Shared Memory Max (shmmax)

From: <miyoshi_at_hpc.bs1.fc.nec.co.jp>
Date: 2002-10-18 11:06:33
Hi,

I suppose '8G' described below means default shmall, that is 524288 * 16K.
And I think there is no restrictions around 8G on IA-64.

Regards,

> > And based on that the total amount of shared memory segment
> > that can be created in IA-64 platform (with 16K page size) is 8G.
> 
> Does this still hold true in newer kernel releases (since 03/2002)?  Is 8G the 
> max for IA64 kernel?
> 
> Thanks,
> Donny
> 
> On Thu March 14 2002 5:13 pm, Seth, Rohit wrote:
> > shmmax is the size of largest shared memory (in bytes) segment that the
> > kernel allows.  System wide value of total shared memory value is given by
> > shmall parameter.  Currently the default value for shmmax is  (extrememly
> > low) 32MB.  And based on that the total amount of shared memory segment
> > that can be created in IA-64 platform (with 16K page size) is 8G. There is
> > no direct relationship between shmmax value and the amount of physical
> > memory available in the system.  Though you will never be able to create a
> > shared memory segment bigger then the total memory (Free RAM+Free SWAP)
> > available on the machine (unless you change the sysctl_overcommit_memory).
> > Besides that, this low default value of 32MB just adds overhead for big
> > memory systems.  It will be nice to change this default value to 2G at
> > least for IA-64 machines.
> >
> > You can also change this value of shm* (shmmax etc.) by writing proper
> > values in /proc/sys/kernel/shm*
> >
> > rohit
> >
> > -----Original Message-----
> > From: Donny Cooper [mailto:dcooper@atcc.necsys.com]
> > Sent: Thursday, March 14, 2002 2:40 PM
> > To: ia64-list@redhat.com; linux-ia64@linuxia64.org
> > Subject: [Linux-ia64] Kernel Shared Memory Max (shmmax)
> >
> >
> >
> > Does the maximum possible shared memory (shmmax) increase with the
> > Enterprise kernel?
> >
> > Below is from doc/sysctl/kernel.txt document.
> > Is this document valid for IA-64 kernel?
> >
> > It seems you can set this value to pretty much anything (even larger than
> > the available memory), so I'm assuming the
> > value gets intelligently truncated to the max supported.  How can I check
> > how much shared mem is available, `free` or
> > `top` just shows what's used, right?
> >
> > ...doc/sysctl/kernel.txt
> > ==============================================================
> >
> > shmmax:
> >
> > This value can be used to query and set the run time limit
> > on the maximum shared memory segment size that can be created.
> > Shared memory segments up to 1Gb are now supported in the
> > kernel.  This value defaults to SHMMAX.
> >
> > ==============================================================
> >
> >
> > Thanks,
> > -----------------------------------
> > Donny Cooper
> > NEC Systems, Inc.
> > Advanced Technical Computing Center
> > dcooper@atcc.necsys.com
> > -----------------------------------
> >
> >
> > _______________________________________________
> > Linux-IA64 mailing list
> > Linux-IA64@linuxia64.org
> > http://lists.linuxia64.org/lists/listinfo/linux-ia64
> >
> >
> >
> > _______________________________________________
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> > ia64-list@redhat.com
> 
> -- 
> =================================
> 	     Donny Cooper
>       NEC Solutions (America), Inc.
> Advanced Technical Computing Center
> 	 ph: +1-281-465-1506
>      Donny.Cooper@NECsam.com
> =================================
> 
> 
> 
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Received on Thu Oct 17 18:03:19 2002

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