AW: Re: RSM Freemained Frames - When do they apply?

[Peter Hunkeler]

> RSM will free frames if available frames are in short supply.
> If you obtain a smaller amount, get it backed, and then release it, you
> may be more likely to observe the frames being retained.


I've changed the program to allocate 8KiB areas instead of 10MiB, and RSM 
decides to keep the frames upon the storage release. IPCS RSMDATA REALFRAME 
lists the freemained frames. Although this feature is pretty much useless for 
the programmer, it's nice to have seen it in action once.


Thanks again, Jim.
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Re: RSM Freemained Frames - When do they apply?

[Jim Mulder]

  It can improve performance for any number of processors, but the value
increases as the number of processors increases.   We do not condition 
its use based on the number of processors. 

Jim Mulder z/OS Diagnosis, Design, Development, Test  IBM Corp. 
Poughkeepsie NY


"IBM Mainframe Discussion List" <IBM-MAIN@LISTSERV.UA.EDU> wrote on 
12/15/2017 07:31:53 AM:

> From: "Christopher Y. Blaicher" <cblaic...@syncsort.com>
> To: IBM-MAIN@LISTSERV.UA.EDU
> Date: 12/15/2017 07:12 PM
> Subject: Re: RSM Freemained Frames - When do they apply?
> Sent by: "IBM Mainframe Discussion List" <IBM-MAIN@LISTSERV.UA.EDU>
> 
> z13 and later.  It works on the z14 also.  I would imagine that IBM 
> saw the problem when they got to a large number of processors.  The 
> overhead internally probably became more expensive that the RSM 
> program overhead.  I don't know, but they may turn it on and off 
> based on the number of processors in the CEC.  Is it worth the RSM 
> overhead if you only have a 4 processor machine verses one with more
> than a 100?  Maybe Jim will comment.
> 
> Chris Blaicher
> Technical Architect
> Mainframe Development
> P: 201-930-8234  |  M: 512-627-3803
> E: cblaic...@syncsort.com
> 
> Syncsort Incorporated
> 2 Blue Hill Plaza #1563
> Pearl River, NY 10965
> www.syncsort.com
> 
> Data quality leader Trillium Software is now a part of Syncsort.
> 
> -Original Message-
> From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU
> ] On Behalf Of Vernooij, Kees (ITOPT1) - KLM
> Sent: Friday, December 15, 2017 2:46 AM
> To: IBM-MAIN@LISTSERV.UA.EDU
> Subject: Re: RSM Freemained Frames - When do they apply?
> 
> Interesting detail: why does this work on z13 only and not on z14?
> 
> Grtn,
> Kees.



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Re: RSM Freemained Frames - When do they apply?

[Christopher Y. Blaicher]

z13 and later.  It works on the z14 also.  I would imagine that IBM saw the 
problem when they got to a large number of processors.  The overhead internally 
probably became more expensive that the RSM program overhead.  I don't know, 
but they may turn it on and off based on the number of processors in the CEC.  
Is it worth the RSM overhead if you only have a 4 processor machine verses one 
with more than a 100?  Maybe Jim will comment.

Chris Blaicher
Technical Architect
Mainframe Development
P: 201-930-8234  |  M: 512-627-3803
E: cblaic...@syncsort.com

Syncsort Incorporated
2 Blue Hill Plaza #1563
Pearl River, NY 10965
www.syncsort.com

Data quality leader Trillium Software is now a part of Syncsort.

-Original Message-
From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On Behalf 
Of Vernooij, Kees (ITOPT1) - KLM
Sent: Friday, December 15, 2017 2:46 AM
To: IBM-MAIN@LISTSERV.UA.EDU
Subject: Re: RSM Freemained Frames - When do they apply?

Interesting detail: why does this work on z13 only and not on z14?

Grtn,
Kees.


> -Original Message-
> From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU]
> On Behalf Of Jim Mulder
> Sent: 15 December, 2017 3:46
> To: IBM-MAIN@LISTSERV.UA.EDU
> Subject: Re: RSM Freemained Frames - When do they apply?
>
>   RSM will free frames if available frames are in short supply.
> If you obtain a smaller amount, get it backed, and then release it,
> you may be more likely to observe the frames being retained.
>
> Jim Mulder z/OS Diagnosis, Design, Development, Test  IBM Corp.
> Poughkeepsie NY
>
> > Running z/OS V2.2 on a z13. "D DIAG" shows FREEMAINEDFRAMES(YES)
> >
> > I'm not trying to solve any specific problem. I'm just curious.
> >
> > I'd like to see the behaviour in different situations when real
> > storage (frames) has been kept as part of RSMs new "freemained
> > frames" feature after the virtual storage has been released
> (freemained).
> >
> > Sample program is obtaining a couple of 10MiB areas, then assessing
> > each page so to make sure it is backed with real storage. Some of
> > the areas are then released again. I was expecting to be able to
> > still access the released pages because RSM decided to keep the
> > frames. Am getting S0C4 instead.
> >
> >
> > Obviously, RSM considers it unnecessary to keep the frames as
> > freemained frames.
> >
> >
> > What, if anything, can I do to have RSM keep the frames when the
> > storage is released?
> > Peter Hunkeler
>
>
>
> --
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> email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN

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Re: RSM Freemained Frames - When do they apply?

[Vernooij, Kees (ITOPT1) - KLM]

Interesting detail: why does this work on z13 only and not on z14?

Grtn,
Kees.


> -Original Message-
> From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On
> Behalf Of Jim Mulder
> Sent: 15 December, 2017 3:46
> To: IBM-MAIN@LISTSERV.UA.EDU
> Subject: Re: RSM Freemained Frames - When do they apply?
> 
>   RSM will free frames if available frames are in short supply.
> If you obtain a smaller amount, get it backed, and then release it, you
> may
> be more likely to observe the frames being retained.
> 
> Jim Mulder z/OS Diagnosis, Design, Development, Test  IBM Corp.
> Poughkeepsie NY
> 
> > Running z/OS V2.2 on a z13. "D DIAG" shows FREEMAINEDFRAMES(YES)
> >
> > I'm not trying to solve any specific problem. I'm just curious.
> >
> > I'd like to see the behaviour in different situations when real
> > storage (frames) has been kept as part of RSMs new "freemained
> > frames" feature after the virtual storage has been released
> (freemained).
> >
> > Sample program is obtaining a couple of 10MiB areas, then assessing
> > each page so to make sure it is backed with real storage. Some of
> > the areas are then released again. I was expecting to be able to
> > still access the released pages because RSM decided to keep the
> > frames. Am getting S0C4 instead.
> >
> >
> > Obviously, RSM considers it unnecessary to keep the frames as
> > freemained frames.
> >
> >
> > What, if anything, can I do to have RSM keep the frames when the
> > storage is released?
> > Peter Hunkeler
> 
> 
> 
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AW: Re: RSM Freemained Frames - When do they apply?

[Peter Hunkeler]

>If you obtain a smaller amount, get it backed, and then release it, you
may be more likely to observe the frames being retained.


Thanks. I (wrongly, it seems) assumed it is more likely to happen with large 
areas.


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AW: Re: AW: Re: RSM Freemained Frames - When do they apply?

[Peter Hunkeler]

>It avoids the issuance of IPTE (an expensive instruction when many CPs are 
>present) for each frame...


I know. Had I not been too lazy to open the PoOp, and read what exactly the 
IPTE does, I had written "it avoids updating the TLB..." instead of "it 
probably avoids...". I promis to do better next time ;-)


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Re: RSM Freemained Frames - When do they apply?

[Jim Mulder]

  RSM will free frames if available frames are in short supply. 
If you obtain a smaller amount, get it backed, and then release it, you 
may
be more likely to observe the frames being retained. 

Jim Mulder z/OS Diagnosis, Design, Development, Test  IBM Corp. 
Poughkeepsie NY

> Running z/OS V2.2 on a z13. "D DIAG" shows FREEMAINEDFRAMES(YES)
> 
> I'm not trying to solve any specific problem. I'm just curious.
> 
> I'd like to see the behaviour in different situations when real 
> storage (frames) has been kept as part of RSMs new "freemained 
> frames" feature after the virtual storage has been released 
(freemained). 
> 
> Sample program is obtaining a couple of 10MiB areas, then assessing 
> each page so to make sure it is backed with real storage. Some of 
> the areas are then released again. I was expecting to be able to 
> still access the released pages because RSM decided to keep the 
> frames. Am getting S0C4 instead.
> 
> 
> Obviously, RSM considers it unnecessary to keep the frames as 
> freemained frames.
> 
> 
> What, if anything, can I do to have RSM keep the frames when the 
> storage is released?
> Peter Hunkeler



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Re: AW: Re: RSM Freemained Frames - When do they apply?

[Ed Jaffe]

On 12/14/2017 1:13 PM, Peter Hunkeler wrote:


The APAR decribes that marking frames as freemained frames avoids signaling all 
processors, which does not scale well with the large number of processors in 
z13 and newer machines. It probably avoids updating the TLBs.


It avoids the issuance of IPTE (an expensive instruction when many CPs 
are present) for each frame...


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AW: Re: RSM Freemained Frames - When do they apply?

[Peter Hunkeler]

>My guess is that the TLB has not been updated yet. That save performance as
the unallocation can wait until all CPs running in the address space have had
normal interrupts to process the changes.




The unallocation can wait until RSM sees a need to put them onto the available 
frames queue. It may well be that such a frame will be reused upon a later 
GETMAIN, when VSM assigns the same virtual address, I would understand.


The APAR decribes that marking frames as freemained frames avoids signaling all 
processors, which does not scale well with the large number of processors in 
z13 and newer machines. It probably avoids updating the TLBs.


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AW: Re: RSM Freemained Frames - When do they apply?

[Peter Hunkeler]

>This not much different from the old situation, where you getmain a page, 
>freemain half of it, so the frame still remains valid and is fully accessible.




Yes, it is much different! In the case you describe, you will find the page is 
allocated in the VSMDATA report. With freemained frames, you not see anything 
in VSMDATA.


Ed confirmed what was my understanding, VSM knows nothing about freemained 
frames. All traces are gone once the storage is freemained (when the page is 
completely freemained).


Earlier this year, when chasing the S0CA problems in COBOL code, I saw 
successful access to some virtual addresses in the system trace but VSMDATA 
said that page is not getmained. I did not understand how this can be, back 
then. I didn't know about freemained frames, yet. Now I understand.


The RSMDATA REALFRAME report marks such freemained frames. Out of curiosity, 
I'd like to once see this in a dump. Hence my question how to create such a 
situation.


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Re: RSM Freemained Frames - When do they apply?

[Binyamin Dissen]

On Thu, 14 Dec 2017 14:04:02 + "Vernooij, Kees (ITOPT1) - KLM"
 wrote:

:>What does this exactly mean: "freemained frames"? Is it just a counter or do 
they refer to specific frames, that are kept at hand in the address space for 
faster assignment of new frame requests?

:>I am not surprised that those frames, if they are "available" at all, are not 
accessible anymore and access is punished with the same 0C4 as any other not 
getmained frame.

My guess is that the TLB has not been updated yet. That save performance as
the unallocation can wait until all CPs running in the address space have had
normal interrupts to process the changes.

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Re: AW: Re: RSM Freemained Frames - When do they apply?

[Ed Jaffe]

On 12/14/2017 6:47 AM, Peter Hunkeler wrote:


See OA46291. The APAR is for z/OS V2.1 and V1.13, it is in the base for z/OS 
V2.2.


Also this great write-up put together by Elipda Tzortatos 
http://publibz.boulder.ibm.com/zoslib/pdf/OA46291.pdf




With this new function, RSM (SRM?) may decide *not* to free the frames that are 
backing some virtual area upon a STORAGE RELEASE or FREEMAIN. It is a 
significant change, IMHO, since a program might continue to (erroneously) 
access storage that has been freed but *not* getting an S0C4-10/11 because the 
frame is still assigned. Or, it may get an S0C4-10/11 at some later point if 
RSM decided to really free some such frame at a later time.


I do not want to build on that function to cheat. I'm wondering what 
information a dump would reveal in such a case. What would VSM tell me? etc.


VSM knows nothing about this. VSMDATA shows what it always showed. This 
is an RSM change only...


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Re: RSM Freemained Frames - When do they apply?

[Vernooij, Kees (ITOPT1) - KLM]

> -Original Message-
> From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On
> Behalf Of Peter Hunkeler
> Sent: 14 December, 2017 15:47
> To: IBM-MAIN@LISTSERV.UA.EDU
> Subject: AW: Re: RSM Freemained Frames - When do they apply?
> 
> 
> >What does this exactly mean: "freemained frames"? Is it just a counter
> or do they refer to specific frames, that are kept at hand in the
> address space for faster assignment of new frame requests?
>  >
> >I am not surprised that those frames, if they are "available" at all,
> are not accessible anymore and access is punished with the same 0C4 as
> any other not getmained frame.
> 
> 
> See OA46291. The APAR is for z/OS V2.1 and V1.13, it is in the base for
> z/OS V2.2.
> 
> 
> With this new function, RSM (SRM?) may decide *not* to free the frames
> that are backing some virtual area upon a STORAGE RELEASE or FREEMAIN.
> It is a significant change, IMHO, since a program might continue to
> (erroneously) access storage that has been freed but *not* getting an
> S0C4-10/11 because the frame is still assigned. Or, it may get an S0C4-
> 10/11 at some later point if RSM decided to really free some such frame
> at a later time.
> 
> 

This not much different from the old situation, where you getmain a page, 
freemain half of it, so the frame still remains valid and is fully accessible.

Kees

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Re: RSM Freemained Frames - When do they apply?

[John McKown]

On Thu, Dec 14, 2017 at 8:47 AM, Peter Hunkeler  wrote:

>
> >What does this exactly mean: "freemained frames"? Is it just a counter or
> do they refer to specific frames, that are kept at hand in the address
> space for faster assignment of new frame requests?
>  >
> >I am not surprised that those frames, if they are "available" at all, are
> not accessible anymore and access is punished with the same 0C4 as any
> other not getmained frame.
>
>
> See OA46291. The APAR is for z/OS V2.1 and V1.13, it is in the base for
> z/OS V2.2.
>
>
> With this new function, RSM (SRM?) may decide *not* to free the frames
> that are backing some virtual area upon a STORAGE RELEASE or FREEMAIN. It
> is a significant change, IMHO, since a program might continue to
> (erroneously) access storage that has been freed but *not* getting an
> S0C4-10/11 because the frame is still assigned. Or, it may get an
> S0C4-10/11 at some later point if RSM decided to really free some such
> frame at a later time.
>

​Ack! Pooie! If it were possible, I would set up my code so that _any_
access to an address which has not been properly "getmain'd" would
_immediately_ S0C4-?? Again, IMO, any access to "unallocated" memory is an
"overrun" situation which should be _fixed_ in the code. The previous may
be influenced from my study (not use) of the IBMi architecture wherein you
simply _cannot_ access something which is not properly allocated. Memory
allocation on the IBMi is "weird".​



>
>
> I do not want to build on that function to cheat. I'm wondering what
> information a dump would reveal in such a case. What would VSM tell me? etc.
>
>
> --
> Peter Hunkeler
>
>
>
>
>
> --
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>



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Maranatha! <><
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AW: Re: RSM Freemained Frames - When do they apply?

[Peter Hunkeler]

>What does this exactly mean: "freemained frames"? Is it just a counter or do 
>they refer to specific frames, that are kept at hand in the address space for 
>faster assignment of new frame requests?
 >
>I am not surprised that those frames, if they are "available" at all, are not 
>accessible anymore and access is punished with the same 0C4 as any other not 
>getmained frame.


See OA46291. The APAR is for z/OS V2.1 and V1.13, it is in the base for z/OS 
V2.2.


With this new function, RSM (SRM?) may decide *not* to free the frames that are 
backing some virtual area upon a STORAGE RELEASE or FREEMAIN. It is a 
significant change, IMHO, since a program might continue to (erroneously) 
access storage that has been freed but *not* getting an S0C4-10/11 because the 
frame is still assigned. Or, it may get an S0C4-10/11 at some later point if 
RSM decided to really free some such frame at a later time.


I do not want to build on that function to cheat. I'm wondering what 
information a dump would reveal in such a case. What would VSM tell me? etc.


--
Peter Hunkeler





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Re: RSM Freemained Frames - When do they apply?

[Vernooij, Kees (ITOPT1) - KLM]

> -Original Message-
> From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On
> Behalf Of Gord Tomlin
> Sent: 14 December, 2017 14:45
> To: IBM-MAIN@LISTSERV.UA.EDU
> Subject: Re: RSM Freemained Frames - When do they apply?
> 
> On 2017-12-14 07:04, Peter Hunkeler wrote:
> > Running z/OS V2.2 on a z13. "D DIAG" shows FREEMAINEDFRAMES(YES)
> >
> > I'm not trying to solve any specific problem. I'm just curious.
> >
> > I'd like to see the behaviour in different situations when real
> storage (frames) has been kept as part of RSMs new "freemained frames"
> feature after the virtual storage has been released (freemained).
> >
> > Sample program is obtaining a couple of 10MiB areas, then assessing
> each page so to make sure it is backed with real storage. Some of the
> areas are then released again. I was expecting to be able to still
> access the released pages because RSM decided to keep the frames. Am
> getting S0C4 instead.
> >
> >
> > Obviously, RSM considers it unnecessary to keep the frames as
> freemained frames.
> >
> >
> > What, if anything, can I do to have RSM keep the frames when the
> storage is released?
> >
> >
> > --
> > Peter Hunkeler
> 
> I wouldn't think IBM would be in a hurry to reveal RSM's algorithm for
> determining whether/when a freemained frame will be discarded. I know
> you are just asking out of curiosity, but any reliance on a freemained
> frame staying available would be like Russian roulette.
> 
> --
> 

What does this exactly mean: "freemained frames"? Is it just a counter or do 
they refer to specific frames, that are kept at hand in the address space for 
faster assignment of new frame requests?

I am not surprised that those frames, if they are "available" at all, are not 
accessible anymore and access is punished with the same 0C4 as any other not 
getmained frame.

Kees.


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e-mail or attachment is strictly prohibited, and may be unlawful. If you have 
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Re: RSM Freemained Frames - When do they apply?

[Gord Tomlin]

On 2017-12-14 07:04, Peter Hunkeler wrote:

Running z/OS V2.2 on a z13. "D DIAG" shows FREEMAINEDFRAMES(YES)

I'm not trying to solve any specific problem. I'm just curious.

I'd like to see the behaviour in different situations when real storage (frames) has been 
kept as part of RSMs new "freemained frames" feature after the virtual storage 
has been released (freemained).

Sample program is obtaining a couple of 10MiB areas, then assessing each page 
so to make sure it is backed with real storage. Some of the areas are then 
released again. I was expecting to be able to still access the released pages 
because RSM decided to keep the frames. Am getting S0C4 instead.


Obviously, RSM considers it unnecessary to keep the frames as freemained frames.


What, if anything, can I do to have RSM keep the frames when the storage is 
released?


--
Peter Hunkeler


I wouldn't think IBM would be in a hurry to reveal RSM's algorithm for 
determining whether/when a freemained frame will be discarded. I know 
you are just asking out of curiosity, but any reliance on a freemained 
frame staying available would be like Russian roulette.


--

Regards, Gord Tomlin
Action Software International
(a division of Mazda Computer Corporation)
Tel: (905) 470-7113, Fax: (905) 470-6507
Support: https://actionsoftware.com/support/

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RSM Freemained Frames - When do they apply?

[Peter Hunkeler]

Running z/OS V2.2 on a z13. "D DIAG" shows FREEMAINEDFRAMES(YES)

I'm not trying to solve any specific problem. I'm just curious.

I'd like to see the behaviour in different situations when real storage 
(frames) has been kept as part of RSMs new "freemained frames" feature after 
the virtual storage has been released (freemained).

Sample program is obtaining a couple of 10MiB areas, then assessing each page 
so to make sure it is backed with real storage. Some of the areas are then 
released again. I was expecting to be able to still access the released pages 
because RSM decided to keep the frames. Am getting S0C4 instead.


Obviously, RSM considers it unnecessary to keep the frames as freemained frames.


What, if anything, can I do to have RSM keep the frames when the storage is 
released?


--
Peter Hunkeler


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