forums.silverfrost.com

[nickb]

Hi
I am having trouble running a large FORTRAN program under VISTA that previously ran OK using XP. The program uses large arrays, but now freezes when trying to open up an open file dialog box. This problem has occurred before using windows 2000, but was not as bad. I have experimented with all possible values of stack and heap using SLINK.
Can someone help me? BTW I have the latest version of the compiler.
Nick Bowring

[PaulLaidler]

This problem has been raised before on this forum but I cannot find the relevants threads. Nor can I remember if there was any clear cut resolution.

If the problem arises from a shortage of memory then under XP you could consider using the 3GB switch in your boot.ini but I do not know if this translates to Vista.

[JohnCampbell]

Paul and others,

I am interested in how the memory limits apply as my next hardware upgrade may go beyond 2gb of memory. My present experience is with 1gb, so these larger numbers are quite a change. It wasn't long ago that I first used files more than 2gb for the out of memory solutions !

Could you provide a reference to extending beyond 2gb, especially for a clearwin+ program. Presumably we can't have single arrays larger than 2gb ?

As an alternative, does anyone know of how to create a virtual disk on a 2gb plus machine to get fast I/O that simply uses the fortran read/write routines to shift information in physical memory, at memory transfer rates ?

Regards John

[PaulLaidler]

John

You will find some information in ftn95.chm if you search for 3GB.

[JohnCampbell]

Paul,

Thanks for the advice. I read the help and have a couple of questions.

Is the addressible length of a single array 1gb, or can this be multiplied by the byte size, ie what is the maximum size of a 1-d real*8 array?
Can a 2 dimensional array go beyond the 1gb limit ?
For example, what is the addressible memory size limit of the following:
Integer*1 i1array(*)
Integer*4 i4array(*)
Integer*4 i4array(4,*)
real*8 r8array(*)

Does the reference to "none of the debugging options" include the /debug option, which mainly provides improved addressing of the source code line location ? I could more understand the resctictions with /check etc.

Any problems with /opt ?

Recent improvement to processor speeds has resulted in an increased relative performance penalty for writing data to disk. To be able to store more information in memory can provide significant improvements. It can take a while to transfer 3gb of info to disk and back again !

I would appreciate your comments,

John

[PaulLaidler]

John

The relevant size (of an array in this context) is the byte size, the number of dimensions is not relevant. You need 4 bytes for each INTEGER*4 element etc. As far as FTN95 is concerned the byte size of an array could be up to 4GB (if you had nothing else but naturally you need space for the program and other data, also the operating system addresses the same 4GB!).

The problem is that Windows normally reserves 2GB for the operating system but with XP (and some other operating systems) this can be decreased to 1GB so that you have a virtual address space of 3GB for applications.

For simplicity the phrase "none of the debugging options" does include /debug because of the way information is passed from the compiler to the linker but you can use 3GB on the SLINK command line to override this. There is no problem with /opt - you automatically get 3GB in this case (provided you have configured your boot.ini for 3GB).

[JohnCampbell]

Paul,

In other words, If I go and buy a new PC with 4gb memory, use the /3gb switch, I can write a program with either

real*8 r8_array(400000000) or
integer*4 i4_array(800000000)

and there will be no problem with the addressing. Both arrays are about 2^31.6 bytes, which is less than 3gb
My DO loop will use an I*4 variable, which should not overflow.
I assume the array should be in COMMON or a MODULE

Any problems with these assumptions ?

I'm wanting to try and reduce the disk I/O and improve performance !

Will this program be paged off to disk at any stage, such as on startup or when the array is first initialised ?

Thanks John

[PaulLaidler]

You do not need to buy a new machine to test this out. If you are using XP then set the /3GB switch in your boot.ini and use your existing RAM. Having more RAM will speed things up. Having less RAM will not stop you from increasing the available memory.

Try a simple test program. In my experience you will be lucky to get more than about 1.5GB in a single array. This is because of all of the other demands on memory usage and limitations (by the operating system) on how chunks of memory are made available to applications.

Within FTN95 default integers are signed 32 bit values so the largest array index for a 1-dimensional array might well be 2**32 - 1. I don't think that FTN95 makes use of INTEGER*8 values in this context (at least not at the moment in the sense of extending the index range). I apologise if this contradicts something I wrote earlier.

[JohnCampbell]

Paul,

I had a go with the following program. I compiled it on my computer (which has ftn95 installed) then copied the .exe's and .dll files to a machine with 4mb memory and the /3gb switch. It ran for 0.8gb and 1.6gb but crashed for 2.4gb. It actually stoped with no message.
I then ran the program on my computer ( with 1gb memory but without the /3gb switch). It ran (slowly !!) for 0.8gb and 1.6gb, but crashed with an access violation for 2.4gb. ( no /3gb switch ?)
I was assuming the ftn95 /link option would enable the /3gb link option ?

I would like to know what is stopping the two machines from running.
Any ideas on what is wrong with the two configurations?
The 4gb machine should have run the program ?
Can I use the /3gb switch on the 1gb memory machine to enable more than 1.6gb virtual memory?

I don't understand why you stated "In my experience you will be lucky to get more than about 1.5GB in a single array". If 3gb is enabled why can't we approach 3gb? Even at 2gb allowable, loosing 0.5gb is a lot of overhead. Or am I missing some other issue ? I thought we discussed the issue of addressing memory and concluded that this limit is 4gb.

If I can solve this, then when I increase the physical memory, that should improve the run time.

I've never been a fan of microsoft's virtual memory management. These tests may give me a better experience of how well it works. Does anyone regularly use virtual memory and achieve resonable run time performance ?

The test program is :

! Last change: JDC 2 Oct 2007 2:03 pm
! Program to test memory sizes
!
module large_array
!
real*10, parameter :: one = 1
real*10, parameter :: two = 2
integer*4, parameter :: thousand = 1000
integer*4, parameter :: million = thousand*thousand
integer*4, parameter :: billion = million*thousand
!
integer*4, parameter :: array_size = 200*million
!
real*8 r8_array(array_size)
end module large_array

use large_array
integer*4 i
real*10 s1, s2, s3
character description*80
!
1001 format (a,b'zzz,zzz,zz#',a)
1002 format (a,es22.15,' (error=',es10.3,')')
1003 format (a,es22.15)
!
i = ((array_size/1024)*/1024
write (description,1001) 'initialising array of ', array_size,' real*8 variables'
call report (description)
write (description,1001) 'Array size = ',i,' mb'
call report (description)
!
do i = 1,array_size
r8_array(i) = i
end do
call report ('array initialised')
!
s3 = array_size
s3 = s3*(s3+one)/two
!
s1 = 0
do i = 1,array_size
s1 = s1 + r8_array(i)
end do
write (description,1002) 'do Sum of array = ',s1, s1-s3
call report (description)
!
s2 = sum (r8_array)
write (description,1002) 'Sum of array = ',s2, s2-s3
call report (description)
!
write (description,1003) 'Answer should be= ',s3
end

subroutine report (description)
!
character description*(*)
real*8 seconds
!
call get_run_time (seconds)
WRITE (*,1011) seconds, trim (description)
!
RETURN
1011 FORMAT (f10.3,2x,a)
END

subroutine get_run_time (seconds)
!
! returns the elapsed time, accurate to .001 seconds (?)
!
real*8 seconds
!
CHARACTER date*8, time*10, zone*5
INTEGER values(
real*8 start_time, x
data start_time / -1 /
!
call DATE_AND_TIME (date, time, zone, values)
!
x = 60.0*60.0*values(5) &
+ 60.0*values(6) &
+ values(7) &
+ 0.001*values(
!
if (start_time < 0) start_time = x
seconds = x - start_time
RETURN
END

[PaulLaidler]

John

I don't think that I can usefully add anything to what I have already written. Here is a summary.

1. You must use 3GB in your boot.ini. The Microsoft documentation will tell you how to do this.

2. You must use a recent version of SLINK. This has options /3GB and /2GB. 3GB is the default for release mode. 2GB is the default of all debugging modes.

3. The amount of RAM that you are using is not relevant except that it will affect the speed of execution. If there is not enough RAM then memory will be swapped in and out from your hard drive.

4. The 3GB of address space that is released by the operating system is for all of the applications that are running on your machine and probably will not be available in one big chunk. Using the 3GB switch in boot.ini will probably increase the amount of memory available to your program but there are other factors (mentioned above) that can affect the outcome.

[JohnCampbell]

Paul,

There are a few points you may be able to clarify.

1. I am generating the test programs on my pc and then transferring them to another pc with 3GB in boot.ini. It uses this for other applications. Do I need 3GB on my machine to generate the test programs ? I only have the compiler installed on my pc. Maybe I should put 3GB into my pc, as I have not heard any adverse comments about performance, due to this change ?
I was puzzled by the 2.4gb program crashing on the /3gb pc, with no error message. It gave the expected access violation window when run on my pc. Do you need to reconfigure pagefile.sys when using 3gb ?

2. I am using [SLINK/Win32 v1.42 Copyright (c) Silverfrost Ltd. 1995-2005]. It has no reference to /3GB or /2GB in the /? help but Ver 1.32 is referred to in the associated ftn95 help documentation.

4. I do not understand your point 4. Why do you say "The 3GB of address space that is released by the operating system is for all of the applications that are running on your machine" ? My understanding is the 3GB allows for each application to have 3gb of virtual address space, and the O/S limited to 1gb of virtual address, common for all applications.
That it "will not be available in one big chunk" is a matter for the O/S's virtual memory management when allocating physical memory.
You also state "Using the 3GB switch in boot.ini will probably increase the amount of memory available to your program but there are other factors (mentioned above) that can affect the outcome." I do not understand what these factors are. I have many programming examples which don't appear to require significant amounts of my 2gb virtual memory. Why can't I get close to the 3gb limit ? Your earlier reference to "you will be lucky to get more than about 1.5GB in a single array" implies a loss of 1.5gb for the rest of the program. This does not appear reasonable. There should be ways of improving this result.

Do any other FTN95 users have experience of using 3GB ?

Thanks again Paul, for your assistance in understanding these issues.

regards John

[JohnCampbell]

I have now tried to run with the 3gb switch on, with Windows XP and 1gb memory. I get a few problems !!

I have two versions of big_array.f95
a 1.5 gb version with "array_size = 200*million"
and a supposed 2.3gb version with "array_size = 300*million"

To generate the program I use the commands
ftn95 big_array
slink big_array.obj /3gb
big_array

( My version of slink is 1.42 and ftn95 is version 4.9.1. I have the ver 5.01 cd but have not yet loaded it up. I'll do that next! )

If I run the 1.5gb version windows task manager shows the virtual memory size as 1,569,039 K but if I run the 2.3gb version, task manager only shows the program as 1,177,048 K and then crashes when the program reaches initiating 1.1 gb

The response is similar if I select the non /3gb statup

Any ideas ?

The latest version of big_array.f95 is:

! Last change: JDC 2 Oct 2007 2:03 pm
! Program to test memory sizes
!
module large_array
!
real*10, parameter :: one = 1
real*10, parameter :: two = 2
real*10, parameter :: eight = 8
integer*4, parameter :: thousand = 1000
integer*4, parameter :: million = thousand*thousand
integer*4, parameter :: billion = million*thousand
!
! integer*4, parameter :: array_size = 200*million ! 1.5 gb works
integer*4, parameter :: array_size = 300*million ! 2.3 gb does not work
!
real*8 r8_array(array_size)
end module large_array

use large_array
integer*4 i, m_100, m
real*10 s1, s2, s3
character description*80
!
1001 format (a,b'zzz,zzz,zz#',a)
1002 format (a,es22.15,' (error=',es10.3,')')
1003 format (a,es22.15)
1004 format ( f5.1,' gb initialised')
!
i = ((array_size/1024)*/1024
write (description,1001) 'initialising array of ', array_size,' real*8 variables'
call report (description)
write (description,1001) 'Array size = ',i,' mb'
call report (description)
!
m_100 = (1024*1024/*100
m = m_100
do i = 1,array_size
m = m-1
if (m <= 0) then
s1 = dble(i) * eight / dble(1024)**3
write (description, 1004) s1
call report (description)
m = m_100
end if
r8_array(i) = i
end do
call report ('array initialised')
!
s3 = array_size
s3 = s3*(s3+one)/two
!
s1 = 0
do i = 1,array_size
s1 = s1 + r8_array(i)
end do
write (description,1002) 'do Sum of array = ',s1, s1-s3
call report (description)
!
s2 = sum (r8_array)
write (description,1002) 'Sum of array = ',s2, s2-s3
call report (description)
!
write (description,1003) 'Answer should be= ',s3
end

subroutine report (description)
!
! returns the time in the form hh:mm pm
!
character description*(*)
real*8 seconds
!
call get_run_time (seconds)
WRITE (*,1011) seconds, trim (description)
!
RETURN
1011 FORMAT (f10.3,2x,a)
END

subroutine get_run_time (seconds)
!
! returns the elapsed time, accurate to .001 seconds (?)
!
real*8 seconds
!
CHARACTER date*8, time*10, zone*5
INTEGER values(
real*8 start_time, x
data start_time / -1 /
!
call DATE_AND_TIME (date, time, zone, values)
!
x = 60.0*60.0*values(5) &
+ 60.0*values(6) &
+ values(7) &
+ 0.001*values(
!
if (start_time < 0) start_time = x
seconds = x - start_time
RETURN
END

[JohnCampbell]

Paul,

I have further investigated the problem.
I am now using ftn95 ver 5.10, but that hasn't changed the results.

I have taken John Horspool's past advice and transferred the array into unlabeled common and used virtual common in slink "/vc" This has not changed the result, but better reports the memory size.

The changed portion of code looks like:
! real*8 r8_array(array_size)
end module large_array

use large_array
!
real*8 r8_array(array_size)
common r8_array

the batch file is :
ftn95 big_array /lis /xref
slink big_array.obj /3gb /map /vc
notepad big_array.map

For different array sizes, the .map reports the following sizes:
Virtual Common information:

Base Length Commit

array_size = 220*million
20000000 68e7784c (run time library decides)
(1678.5Mb)

array_size = 260*million
20000000 7bfa484c (run time library decides)
(1983.6Mb)

array_size = 270*million
20000000 405f7e4c (run time library decides)
(1030.0Mb)

This appears to place a limit of 2gb on the single array. I don't know if this is also a limit on common, or all common, but this is not achieving more than 2gb, unlike an earlier implied 4gb limit.
.. "As far as FTN95 is concerned the byte size of an array could be up to 4GB"

Where is this limit applied and how can it be overcome ?

Regards John

[PaulLaidler]

John

"As far as FTN95 is concerned the byte size of an array could be up to 4GB"

I have corrected this statement. In some, if not all situations, the limit could be 2GB (the upper bound for signed INTEGER*4 values).

The point is that the operating system is usually more restrictive than FTN95 in this context.

The operating system allocates memory (up to 2 or 3GB) for all applications that are currently running on your machine. I cannot think of another way to say this. You can use the Task Manager to see what is currently running.

As far as I know SLINK does not need to have 3GB in the boot.ini when linking.

If SLINK does not complain about the use of /2GB or /3GB then the version number of SLINK will be OK.

When your FTN95 application runs, it asks the operating system for chunks of memory. There will be limitations within FTN95 on the size that can be requested and limitations provided by the operating system on what requests can be granted.

If you use 3GB in your boot.ini then you should see an improvement. I cannot say more than this.

[JohnCampbell]

Paul,

I have proceeded to try and get a program to work. I am hitting a limit of 2gb for all variables, either as common, virtual common or a mixture of big arrays in a module and in common. The program will not load, giving either a negative common size or not being a valid win32 program.
I tried to split the arrays into two, but was limited in how I could manage them in slink.
I will continue to experiment and try to get it working. It may take a while !

Has anyone out there successfully used /3gb and created a program that uses more than 2gb of data ?

Regards John