Problem with mlockall() and Threads: memory usage

Problem with mlockall() and Threads: memory usage

[Terry Barnaby]

Hi,

We have a problem with a soft real-time program that uses mlockall
to improve its latency.

The basic problem, which can be seen with a simple test example, is
that if we have a program that uses a large amount of memory, uses multiple
threads and uses mlockall() the physical memory usage goes through the
roof. This problem/feature is present using RedHat 7.3 (2.4.x libc user level
threads), RedHat 9 (2.4.20 kernel threads) and Fedora Core 2 (2.6.5).

Our simple test program first does a mlockall(MCL_CURRENT | MCL_FUTURE),
mallocs 10MBytes and then creates 8 threads all which pause.

The memory usage with the mlockall() call is:
  PID TTY      STAT   TIME  MAJFL   TRS   DRS  RSS %MEM COMMAND
2251 pts/1    SL     0:00      0     2 95921 95924 37.3 ./t2 8

The memory usage without the mlockall() call is:
  PID TTY      STAT   TIME  MAJFL   TRS   DRS  RSS %MEM COMMAND
2275 pts/1    S      0:00      0     2 95929 11152  4.3 ./t2 8

It appears that the kernel is allocating physical memory for each
of the Threads shared data area's rather than allocating just
the one shared area.

Are we doing something wrong ?
Is this the correct behaviour ?
Is this a kernle or glibc bug ?

Example code follows:

Terry

/*******************************************************************************
  *	T2.c		Test Threads
  *			T.Barnaby,	BEAM Ltd,	18/5/04
  *******************************************************************************
  */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/mman.h>
#include <sys/statfs.h>

const int	memSize = (10 * 1024*1024);

void* threadFunc(void* arg){
	while(1){
		printf("Thread::function: loop: Pid(%d)\n", getpid());
		pause();
	}
}

void test1(int n){
	pthread_t*	threads;
	void*		mem;
	int		i;

	threads = (pthread_t*)malloc(n * sizeof(pthread_t));
	mem = malloc(memSize);
	memset(mem, 0, memSize);
	printf("Mem: %p\n", mem);

	for(i = 0; i < n; i++){
		pthread_create(&threads[i], 0, threadFunc, 0);
	}		
	pause();
}


int main(int argc, char** argv){
	if(argc != 2){
		fprintf(stderr, "Usage: t2 <numberOfThreads>\n");
		return 1;
	}
	
#ifndef ZAP
	// Lock in all of the pages of this application
	if(mlockall(MCL_CURRENT | MCL_FUTURE) < 0)
		fprintf(stderr, "Warning: unable to lock in memory pages\n");
#endif

	test1(atoi(argv[1]));
	return 0;
}

-- 
Dr Terry Barnaby                     BEAM Ltd
Phone: +44 1454 324512               Northavon Business Center, Dean Rd
Fax:   +44 1454 313172               Yate, Bristol, BS37 5NH, UK
Email: terry@beam.ltd.uk             Web: www.beam.ltd.uk
BEAM for: Visually Impaired X-Terminals, Parallel Processing, Software
                       "Tandems are twice the fun !"

Re: Problem with mlockall() and Threads: memory usage

[Terry Barnaby]

Thanks for that.
I have done some more investigating, and on my system (Standard RedHat 9)
the stack ulimit is set to 8192 KBytes. So it appears that the thread
library/kernel threads pre-allocates, and writes to, 8129 KBytes of stack per
thread and so then mlockall() locks all of this in memory.

Should'nt the Thread library grow the stack rather than preallocate it all even
with mlockall() like malloc ?

I also notice that if I set the pre-thread stack with pthread_attr_setstacksize()
this sets the hard limit for stack size rather than the initial stack size
as stated in the pthread.h include file. Maybe there is another way to
set the initial stack size per thread ?

Anyway I presume this stack manipulation is done in the user level threads
library rather than the kernel (even on NPTL). So I guess I should move this
question to the list for Linux Threads. Any ideas where this list is ?

Cheers

Terry

Mike Black wrote:
> I compiled your program on my system and it behaves like you would expect.  Looks like about 2Meg per thread overhead..
> t5 is with mlock and t5a is without -- I've attached a static compile of t5 so you can test it on your system.
> That way it will tell whether it's just your compiler/library setup or the OS.
> I'm running Linux 2.6.6, libc-2.3.2, libpthread-0.10
> 
> The zip file password is "t5"
> 
> 
> ----- Original Message ----- 
> From: "Terry Barnaby" <terry1@beam.ltd.uk>
> To: <linux-kernel@vger.kernel.org>
> Sent: Tuesday, May 18, 2004 6:10 AM
> Subject: Problem with mlockall() and Threads: memory usage
> 
> 
> 
>>Hi,
>>
>>We have a problem with a soft real-time program that uses mlockall
>>to improve its latency.
>>
>>The basic problem, which can be seen with a simple test example, is
>>that if we have a program that uses a large amount of memory, uses multiple
>>threads and uses mlockall() the physical memory usage goes through the
>>roof. This problem/feature is present using RedHat 7.3 (2.4.x libc user level
>>threads), RedHat 9 (2.4.20 kernel threads) and Fedora Core 2 (2.6.5).
>>
>>Our simple test program first does a mlockall(MCL_CURRENT | MCL_FUTURE),
>>mallocs 10MBytes and then creates 8 threads all which pause.
>>
>>The memory usage with the mlockall() call is:
>>  PID TTY      STAT   TIME  MAJFL   TRS   DRS  RSS %MEM COMMAND
>>2251 pts/1    SL     0:00      0     2 95921 95924 37.3 ./t2 8
>>
>>The memory usage without the mlockall() call is:
>>  PID TTY      STAT   TIME  MAJFL   TRS   DRS  RSS %MEM COMMAND
>>2275 pts/1    S      0:00      0     2 95929 11152  4.3 ./t2 8
>>
>>It appears that the kernel is allocating physical memory for each
>>of the Threads shared data area's rather than allocating just
>>the one shared area.
>>
>>Are we doing something wrong ?
>>Is this the correct behaviour ?
>>Is this a kernle or glibc bug ?
>>
>>Example code follows:
>>
>>Terry
>>
>>/*******************************************************************************
>>  * T2.c Test Threads
>>  * T.Barnaby, BEAM Ltd, 18/5/04
>>  *******************************************************************************
>>  */
>>#include <stdio.h>
>>#include <stdlib.h>
>>#include <string.h>
>>#include <unistd.h>
>>#include <pthread.h>
>>#include <sys/mman.h>
>>#include <sys/statfs.h>
>>
>>const int memSize = (10 * 1024*1024);
>>
>>void* threadFunc(void* arg){
>>while(1){
>>printf("Thread::function: loop: Pid(%d)\n", getpid());
>>pause();
>>}
>>}
>>
>>void test1(int n){
>>pthread_t* threads;
>>void* mem;
>>int i;
>>
>>threads = (pthread_t*)malloc(n * sizeof(pthread_t));
>>mem = malloc(memSize);
>>memset(mem, 0, memSize);
>>printf("Mem: %p\n", mem);
>>
>>for(i = 0; i < n; i++){
>>pthread_create(&threads[i], 0, threadFunc, 0);
>>} 
>>pause();
>>}
>>
>>
>>int main(int argc, char** argv){
>>if(argc != 2){
>>fprintf(stderr, "Usage: t2 <numberOfThreads>\n");
>>return 1;
>>}
>>
>>#ifndef ZAP
>>// Lock in all of the pages of this application
>>if(mlockall(MCL_CURRENT | MCL_FUTURE) < 0)
>>fprintf(stderr, "Warning: unable to lock in memory pages\n");
>>#endif
>>
>>test1(atoi(argv[1]));
>>return 0;
>>}
>>
>>-- 
>>Dr Terry Barnaby                     BEAM Ltd
>>Phone: +44 1454 324512               Northavon Business Center, Dean Rd
>>Fax:   +44 1454 313172               Yate, Bristol, BS37 5NH, UK
>>Email: terry@beam.ltd.uk             Web: www.beam.ltd.uk
>>BEAM for: Visually Impaired X-Terminals, Parallel Processing, Software
>>                       "Tandems are twice the fun !"
>>-
>>To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>>the body of a message to majordomo@vger.kernel.org
>>More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>Please read the FAQ at  http://www.tux.org/lkml/

-- 
Dr Terry Barnaby                     BEAM Ltd
Phone: +44 1454 324512               Northavon Business Center, Dean Rd
Fax:   +44 1454 313172               Yate, Bristol, BS37 5NH, UK
Email: terry@beam.ltd.uk             Web: www.beam.ltd.uk
BEAM for: Visually Impaired X-Terminals, Parallel Processing, Software
                       "Tandems are twice the fun !"

RE: Problem with mlockall() and Threads: memory usage

[David Schwartz]

> Thanks for that.
> I have done some more investigating, and on my system (Standard RedHat 9)
> the stack ulimit is set to 8192 KBytes. So it appears that the thread
> library/kernel threads pre-allocates, and writes to, 8129 KBytes
> of stack per
> thread and so then mlockall() locks all of this in memory.
>
> Should'nt the Thread library grow the stack rather than
> preallocate it all even
> with mlockall() like malloc ?

	I thought you wanted improved latency. Surely having to find a page for you
when your stack grows will add unpredictable latency. So, no, the thread
library should reserve the stack when 'mlockall(MCL_FUTURE)' is specified.

	I do agree that having an 'initial stack size' in additional to a 'maximum
stack size' would be a good idea. The former good for application that are
concerned about physical memory usage and the latter for applications
concerned about virtual memory usage.

	DS

Re: Problem with mlockall() and Threads: memory usage

[Terry Barnaby]

Hi David,

We do want improved latency, but with reasonable memory usage. This is
a soft real-time system. At the moment the memory usage is far too high in
our application.

With 20 threads runing the system will lock 160MBytes of memory just for stack
space (8 MBytes each), although the application probably only needs 2MByte in
total.
We can reduce the maximum stack size per thread, but then if a thread
increases its stack size beyond this the application will crash with a
segment fault, not good ...

For our use, mapping in physical memory as required for a growing stack would be
a good compromise between latency and memory usage. Once the system has run the
worker threads for a short time all of the needed stack memory will be locked in
and latency will be controlled. If a thread needs more memory for stack in a particular
instance, there will be a latency hit but this would be acceptable and
much better than a crash.

Terry

David Schwartz wrote:
>>Thanks for that.
>>I have done some more investigating, and on my system (Standard RedHat 9)
>>the stack ulimit is set to 8192 KBytes. So it appears that the thread
>>library/kernel threads pre-allocates, and writes to, 8129 KBytes
>>of stack per
>>thread and so then mlockall() locks all of this in memory.
>>
>>Should'nt the Thread library grow the stack rather than
>>preallocate it all even
>>with mlockall() like malloc ?
> 
> 
> 	I thought you wanted improved latency. Surely having to find a page for you
> when your stack grows will add unpredictable latency. So, no, the thread
> library should reserve the stack when 'mlockall(MCL_FUTURE)' is specified.
> 
> 	I do agree that having an 'initial stack size' in additional to a 'maximum
> stack size' would be a good idea. The former good for application that are
> concerned about physical memory usage and the latter for applications
> concerned about virtual memory usage.
> 
> 	DS
> 
> 
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
> 

-- 
Dr Terry Barnaby                     BEAM Ltd
Phone: +44 1454 324512               Northavon Business Center, Dean Rd
Fax:   +44 1454 313172               Yate, Bristol, BS37 5NH, UK
Email: terry@beam.ltd.uk             Web: www.beam.ltd.uk
BEAM for: Visually Impaired X-Terminals, Parallel Processing, Software
                       "Tandems are twice the fun !"

Re: Problem with mlockall() and Threads: memory usage

[Elladan]

On Wed, May 19, 2004 at 09:45:27AM +0100, Terry Barnaby wrote:
> Hi David,
> 
> We do want improved latency, but with reasonable memory usage. This is
> a soft real-time system. At the moment the memory usage is far too
> high in our application.
> 
> With 20 threads runing the system will lock 160MBytes of memory just
> for stack space (8 MBytes each), although the application probably
> only needs 2MByte in total.  We can reduce the maximum stack size per
> thread, but then if a thread increases its stack size beyond this the
> application will crash with a segment fault, not good ...
> 
> For our use, mapping in physical memory as required for a growing
> stack would be a good compromise between latency and memory usage.
> Once the system has run the worker threads for a short time all of the
> needed stack memory will be locked in and latency will be controlled.
> If a thread needs more memory for stack in a particular instance,
> there will be a latency hit but this would be acceptable and much
> better than a crash.

It sounds to me like you have a really special-purpose situation here.
You want to minimize the amount of memory used, but you may have deep
stacks of unknown depth and you can't grow them safely without incurring
latency.

It seems to me that you really should just figure out how much stack
your app really needs and set your limits appropriately.  If your
program requires indeterminate stack depth, you should fix it so it
doesn't.

If you really, really want random memory allocations and memory locking
at the same time, you could implement your own mlockall solution with
your own stack manager.  You could do an mlockall(MCL_CURRENT) with
small stack reserves, and then manually go and remap your stack space
the way you want it.  Of course, you'd need your own memory allocator if
you ever allocate more non-stack memory, but you'll need that anyway.

-J

> David Schwartz wrote:
> >>Thanks for that.
> >>I have done some more investigating, and on my system (Standard RedHat 9)
> >>the stack ulimit is set to 8192 KBytes. So it appears that the thread
> >>library/kernel threads pre-allocates, and writes to, 8129 KBytes
> >>of stack per
> >>thread and so then mlockall() locks all of this in memory.
> >>
> >>Should'nt the Thread library grow the stack rather than
> >>preallocate it all even
> >>with mlockall() like malloc ?
> >
> >
> >	I thought you wanted improved latency. Surely having to find a page 
> >	for you
> >when your stack grows will add unpredictable latency. So, no, the thread
> >library should reserve the stack when 'mlockall(MCL_FUTURE)' is specified.
> >
> >	I do agree that having an 'initial stack size' in additional to a 
> >	'maximum
> >stack size' would be a good idea. The former good for application that are
> >concerned about physical memory usage and the latter for applications
> >concerned about virtual memory usage.
> >
> >	DS
> >
> >
> >-
> >To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> >the body of a message to majordomo@vger.kernel.org
> >More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >Please read the FAQ at  http://www.tux.org/lkml/
> >
> 
> -- 
> Dr Terry Barnaby                     BEAM Ltd
> Phone: +44 1454 324512               Northavon Business Center, Dean Rd
> Fax:   +44 1454 313172               Yate, Bristol, BS37 5NH, UK
> Email: terry@beam.ltd.uk             Web: www.beam.ltd.uk
> BEAM for: Visually Impaired X-Terminals, Parallel Processing, Software
>                       "Tandems are twice the fun !"
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

Re: Problem with mlockall() and Threads: memory usage

[Terry Barnaby]

Hi Elladan,

Thanks for the responce, I don't think we have a really special-purpose
situation here. The application is relatively complex it that it
uses CORBA as well as many other libraries. We cannot hope to
calculate the necessary total stack usage, just make an educated guess
based on observed stack usage during running. It is very likely
that the stack usage will be small, and we can safely set the stack size
small, however we cannot garantee this. Normally VM allows programmers
flexibility with memory size limitations.
It seems inconsistant that when using mlockall() newly malloced memory will
be paged in as required but stacks are fixed into memory. Both of these
mechanisems involve dynamically extending the processes memory. I would have
thought it better that stacks followed the malloc() model in that memory
pages are only allocated as required. A system that needed to guarantee
no page faults could preallocate the stack easily as it would have to
with the heap. I do understand that this could be dificult to achieve
however.

Anyway cheers for the response and pointers.

Cheers

Terry

Some info gained for those reading this thread:
1. If you have a threaded application and you use
	mlockall(MCL_CURRENT | MCL_FUTURE) then the full amount
	of each threads	preallocated stack will be mapped into
	physical memory.
2. If you use pthread_create(&t, NULL, func, 0) then RedHat 9
	will allocate 8MBytes of stack per thread. (Possibly
	the amount set by the processes stack ulimit ?)
3. If you use pthread_create(&t, &a, func, 0) and set up the
	attributes with pthread_attr_init(&a) then RedHat 9
	will allocate 2MBytes to each thread. The pthreads manual
	states that using pthread_create() with attibutes set
	using pthread_attr_init() is the same as using NULL to
	pthread_create() this is WRONG. Also using pthread_attr_init()
	will sets the threads scheduler to SCHED_OTHER rather
	than "inherit" the parents scheduler config as passing
	NULL to pthread_create() does.

Elladan wrote:
> On Wed, May 19, 2004 at 09:45:27AM +0100, Terry Barnaby wrote:
> 
>>Hi David,
>>
>>We do want improved latency, but with reasonable memory usage. This is
>>a soft real-time system. At the moment the memory usage is far too
>>high in our application.
>>
>>With 20 threads runing the system will lock 160MBytes of memory just
>>for stack space (8 MBytes each), although the application probably
>>only needs 2MByte in total.  We can reduce the maximum stack size per
>>thread, but then if a thread increases its stack size beyond this the
>>application will crash with a segment fault, not good ...
>>
>>For our use, mapping in physical memory as required for a growing
>>stack would be a good compromise between latency and memory usage.
>>Once the system has run the worker threads for a short time all of the
>>needed stack memory will be locked in and latency will be controlled.
>>If a thread needs more memory for stack in a particular instance,
>>there will be a latency hit but this would be acceptable and much
>>better than a crash.
> 
> 
> It sounds to me like you have a really special-purpose situation here.
> You want to minimize the amount of memory used, but you may have deep
> stacks of unknown depth and you can't grow them safely without incurring
> latency.
> 
> It seems to me that you really should just figure out how much stack
> your app really needs and set your limits appropriately.  If your
> program requires indeterminate stack depth, you should fix it so it
> doesn't.
> 
> If you really, really want random memory allocations and memory locking
> at the same time, you could implement your own mlockall solution with
> your own stack manager.  You could do an mlockall(MCL_CURRENT) with
> small stack reserves, and then manually go and remap your stack space
> the way you want it.  Of course, you'd need your own memory allocator if
> you ever allocate more non-stack memory, but you'll need that anyway.
> 
> -J
> 
> 
>>David Schwartz wrote:
>>
>>>>Thanks for that.
>>>>I have done some more investigating, and on my system (Standard RedHat 9)
>>>>the stack ulimit is set to 8192 KBytes. So it appears that the thread
>>>>library/kernel threads pre-allocates, and writes to, 8129 KBytes
>>>>of stack per
>>>>thread and so then mlockall() locks all of this in memory.
>>>>
>>>>Should'nt the Thread library grow the stack rather than
>>>>preallocate it all even
>>>>with mlockall() like malloc ?
>>>
>>>
>>>	I thought you wanted improved latency. Surely having to find a page 
>>>	for you
>>>when your stack grows will add unpredictable latency. So, no, the thread
>>>library should reserve the stack when 'mlockall(MCL_FUTURE)' is specified.
>>>
>>>	I do agree that having an 'initial stack size' in additional to a 
>>>	'maximum
>>>stack size' would be a good idea. The former good for application that are
>>>concerned about physical memory usage and the latter for applications
>>>concerned about virtual memory usage.
>>>
>>>	DS
>>>
>>>
>>>-
>>>To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>>>the body of a message to majordomo@vger.kernel.org
>>>More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>Please read the FAQ at  http://www.tux.org/lkml/
>>>
>>
>>-- 
>>Dr Terry Barnaby                     BEAM Ltd
>>Phone: +44 1454 324512               Northavon Business Center, Dean Rd
>>Fax:   +44 1454 313172               Yate, Bristol, BS37 5NH, UK
>>Email: terry@beam.ltd.uk             Web: www.beam.ltd.uk
>>BEAM for: Visually Impaired X-Terminals, Parallel Processing, Software
>>                      "Tandems are twice the fun !"
>>-
>>To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>>the body of a message to majordomo@vger.kernel.org
>>More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>Please read the FAQ at  http://www.tux.org/lkml/
> 
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
> 

-- 
Dr Terry Barnaby                     BEAM Ltd
Phone: +44 1454 324512               Northavon Business Center, Dean Rd
Fax:   +44 1454 313172               Yate, Bristol, BS37 5NH, UK
Email: terry@beam.ltd.uk             Web: www.beam.ltd.uk
BEAM for: Visually Impaired X-Terminals, Parallel Processing, Software
                       "Tandems are twice the fun !"

Re: Problem with mlockall() and Threads: memory usage

[Terry Barnaby]

Hi Elladan,

Thanks for the responce, I don't think we have a really special-purpose
situation here. The application is relatively complex it that it
uses CORBA as well as many other libraries. We cannot hope to
calculate the necessary total stack usage, just make an educated guess
based on observed stack usage during running. It is very likely
that the stack usage will be small, and we can safely set the stack size
small, however we cannot garantee this. Normally VM allows programmers
flexibility with memory size limitations.
It seems inconsistant that when using mlockall() newly malloced memory will
be paged in as required but stacks are fixed into memory. Both of these
mechanisems involve dynamically extending the processes memory. I would have
thought it better that stacks followed the malloc() model in that memory
pages are only allocated as required. A system that needed to guarantee
no page faults could preallocate the stack easily as it would have to
with the heap. I do understand that this could be dificult to achieve
however.

Anyway cheers for the response and pointers.

Cheers

Terry

Some info gained for those reading this thread:
1. If you have a threaded application and you use
	mlockall(MCL_CURRENT | MCL_FUTURE) then the full amount
	of each threads	preallocated stack will be mapped into
	physical memory.
2. If you use pthread_create(&t, NULL, func, 0) then RedHat 9
	will allocate 8MBytes of stack per thread. (Possibly
	the amount set by the processes stack ulimit ?)
3. If you use pthread_create(&t, &a, func, 0) and set up the
	attributes with pthread_attr_init(&a) then RedHat 9
	will allocate 2MBytes to each thread. The pthreads manual
	states that using pthread_create() with attibutes set
	using pthread_attr_init() is the same as using NULL to
	pthread_create() this is WRONG. Also using pthread_attr_init()
	will sets the threads scheduler to SCHED_OTHER rather
	than "inherit" the parents scheduler config as passing
	NULL to pthread_create() does.

Elladan wrote:
> On Wed, May 19, 2004 at 09:45:27AM +0100, Terry Barnaby wrote:
> 
>>Hi David,
>>
>>We do want improved latency, but with reasonable memory usage. This is
>>a soft real-time system. At the moment the memory usage is far too
>>high in our application.
>>
>>With 20 threads runing the system will lock 160MBytes of memory just
>>for stack space (8 MBytes each), although the application probably
>>only needs 2MByte in total.  We can reduce the maximum stack size per
>>thread, but then if a thread increases its stack size beyond this the
>>application will crash with a segment fault, not good ...
>>
>>For our use, mapping in physical memory as required for a growing
>>stack would be a good compromise between latency and memory usage.
>>Once the system has run the worker threads for a short time all of the
>>needed stack memory will be locked in and latency will be controlled.
>>If a thread needs more memory for stack in a particular instance,
>>there will be a latency hit but this would be acceptable and much
>>better than a crash.
> 
> 
> It sounds to me like you have a really special-purpose situation here.
> You want to minimize the amount of memory used, but you may have deep
> stacks of unknown depth and you can't grow them safely without incurring
> latency.
> 
> It seems to me that you really should just figure out how much stack
> your app really needs and set your limits appropriately.  If your
> program requires indeterminate stack depth, you should fix it so it
> doesn't.
> 
> If you really, really want random memory allocations and memory locking
> at the same time, you could implement your own mlockall solution with
> your own stack manager.  You could do an mlockall(MCL_CURRENT) with
> small stack reserves, and then manually go and remap your stack space
> the way you want it.  Of course, you'd need your own memory allocator if
> you ever allocate more non-stack memory, but you'll need that anyway.
> 
> -J
> 
> 
>>David Schwartz wrote:
>>
>>>>Thanks for that.
>>>>I have done some more investigating, and on my system (Standard RedHat 9)
>>>>the stack ulimit is set to 8192 KBytes. So it appears that the thread
>>>>library/kernel threads pre-allocates, and writes to, 8129 KBytes
>>>>of stack per
>>>>thread and so then mlockall() locks all of this in memory.
>>>>
>>>>Should'nt the Thread library grow the stack rather than
>>>>preallocate it all even
>>>>with mlockall() like malloc ?
>>>
>>>
>>>	I thought you wanted improved latency. Surely having to find a page 
>>>	for you
>>>when your stack grows will add unpredictable latency. So, no, the thread
>>>library should reserve the stack when 'mlockall(MCL_FUTURE)' is specified.
>>>
>>>	I do agree that having an 'initial stack size' in additional to a 
>>>	'maximum
>>>stack size' would be a good idea. The former good for application that are
>>>concerned about physical memory usage and the latter for applications
>>>concerned about virtual memory usage.
>>>
>>>	DS
>>>
>>>
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>>>
>>
>>-- 
>>Dr Terry Barnaby                     BEAM Ltd
>>Phone: +44 1454 324512               Northavon Business Center, Dean Rd
>>Fax:   +44 1454 313172               Yate, Bristol, BS37 5NH, UK
>>Email: terry@beam.ltd.uk             Web: www.beam.ltd.uk
>>BEAM for: Visually Impaired X-Terminals, Parallel Processing, Software
>>                      "Tandems are twice the fun !"
>>-
>>To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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> 
> -
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> 

-- 
Dr Terry Barnaby                     BEAM Ltd
Phone: +44 1454 324512               Northavon Business Center, Dean Rd
Fax:   +44 1454 313172               Yate, Bristol, BS37 5NH, UK
Email: terry@beam.ltd.uk             Web: www.beam.ltd.uk
BEAM for: Visually Impaired X-Terminals, Parallel Processing, Software
                       "Tandems are twice the fun !"