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

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

[Donny Cooper]

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
-----------------------------------

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

[Seth, Rohit]

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

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

[David Mosberger]

>>>>> On Thu, 14 Mar 2002 15:13:35 -0800, "Seth, Rohit" <rohit.seth@intel.com> said:

  Rohit> Besides that, this low default
  Rohit> value of 32MB just adds overhead for big memory systems.  It
  Rohit> will be nice to change this default value to 2G at least for
  Rohit> IA-64 machines.

I agree; it always struck me as a curiosity from days long gone... ;-)

	--david

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

[Seth, Rohit]

David,

If you need any preference of value for shmmax, then please go with 4G
(though there are utilities that expect size of shared memory segment to be
only int :) but that should be fixed seperately). Could you please make this
change in your next patch.

thanks,
rohit


-----Original Message-----
From: David Mosberger [mailto:davidm@napali.hpl.hp.com]
Sent: Thursday, March 14, 2002 3:32 PM
To: Seth, Rohit
Cc: 'dcooper@atcc.necsys.com'; ia64-list@redhat.com;
linux-ia64@linuxia64.org
Subject: RE: [Linux-ia64] Kernel Shared Memory Max (shmmax)


>>>>> On Thu, 14 Mar 2002 15:13:35 -0800, "Seth, Rohit"
<rohit.seth@intel.com> said:

  Rohit> Besides that, this low default
  Rohit> value of 32MB just adds overhead for big memory systems.  It
  Rohit> will be nice to change this default value to 2G at least for
  Rohit> IA-64 machines.

I agree; it always struck me as a curiosity from days long gone... ;-)

	--david

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

[miyoshi]

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
> >
> >
> >
> > _______________________________________________
> > ia64-list mailing list
> > ia64-list@redhat.com
> 
> -- 
> ================> 	     Donny Cooper
>       NEC Solutions (America), Inc.
> Advanced Technical Computing Center
> 	 ph: +1-281-465-1506
>      Donny.Cooper@NECsam.com
> ================> 
> 
> 
> _______________________________________________
> ia64-list mailing list
> ia64-list@redhat.com
> https://listman.redhat.com/mailman/listinfo/ia64-list
> 

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

[Seth, Rohit]

The restriction is coming out of default parameters set in Linux (file
include/linux/shm.h).
These values could be changed through /proc/sys/kernel/shm* interface.  And
if a site permanentlly wants to have higher values for this parameters then
that can be achieved by something like rc.local

Have not seen any distribution increasing the default values for IA-64 yet.

rohit


> -----Original Message-----
> From: miyoshi@hpc.bs1.fc.nec.co.jp 
> [mailto:miyoshi@hpc.bs1.fc.nec.co.jp] 
> Sent: Thursday, October 17, 2002 6:07 PM
> To: rohit.seth@intel.com; dcooper@atcc.necsys.com
> Cc: ia64-list@redhat.com; linux-ia64@linuxia64.org; 
> jfredin@atcc.necsys.com
> Subject: Re: [Linux-ia64] Kernel Shared Memory Max (shmmax)
> 
> 
> 
> 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
> > >
> > >
> > >
> > > _______________________________________________
> > > ia64-list mailing list
> > > ia64-list@redhat.com
> > 
> > --
> > ================> > 	     Donny Cooper
> >       NEC Solutions (America), Inc.
> > Advanced Technical Computing Center
> > 	 ph: +1-281-465-1506
> >      Donny.Cooper@NECsam.com
> > ================> > 
> > 
> > 
> > _______________________________________________
> > ia64-list mailing list
> > ia64-list@redhat.com 
> > https://listman.redhat.com/mailman/listinfo/ia64-list
> > 
> 

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

[Seth, Rohit]

         .....


> Sorry, but obviously I'm still confused here.  Is there a max 
> of 8GB or any 
> other value that I cannot exceed on IA-64 systems?
> 

There is no limit of 8G on shared memory segments from IA-64 arch.  As long
as you are keeping the values shm* parameters large in kernel, you should be
able to go to few TB range.  If you have bigger memory machine then go ahead
and bump up the values of these shm parameters.  (Though I think ipcs is
probably still broken and will not print the correct values), but you should
actually be able to use these big segments.

rohit