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Memory Management again [message #1668]

Sun, 19 February 2006 10:34

atomic
Messages: 8
Registered: January 2006

Junior Member

Hi,

i read many postings about memory restrictions and guaranteed memory sizes, so i figured out some
values for standard memory sizes.

VMGUARPAGES="32768:2147483647"	// 128MB Guaranteed
VMGUARPAGES="65536:2147483647"	// 256MB Guaranteed
VMGUARPAGES="131072:2147483647"	// 512MB Guaranteed

PRIVVMPAGES="64000:65536"	// 256MB Burst
PRIVVMPAGES="128000:131072"	// 512MB Burst
PRIVVMPAGES="256000:262140"	// 1024MB Burst

Calculation:
VMGUARPAGES and PRIVVMPAGES values are given in memory pages.
One memory page holds 4096Bits or 4Kbyte on a x86-System.
65536 Pages * 4Kbyte = 262144Kbyte = 256Mbyte

Where "guaranteed" means the absolute minimum of available RAM, even if the node is heavily loaded,
and "burst" means the limit of allocatable RAM if there is enough free.

Here is a beancounter output of a VPS with 256Mbyte guaranteed and 1024MByte burst memory:

Version: 2.5
       uid  resource           held    maxheld    barrier      limit    failcnt
         3: kmemsize        3532503    4198588   16979722   18677694          0
            lockedpages           0          0        829        829          0
            privvmpages      147040     149045     256000     262140          0
            shmpages          11417      11433      31096      31096          0
            dummy                 0          0          0          0          0
            numproc             100        117        800        800          0
            physpages         32964      34396          0 2147483647          0
            vmguarpages           0          0      65535 2147483647          0
            oomguarpages      32964      34396     310967 2147483647          0
            numtcpsock           24         25        800        800          0
            numflock              7         10        662        728          0
            numpty                1          1         80         80          0
            numsiginfo            0          2       1024       1024          0
            tcpsndbuf          4456      16744    2383107    5659907          0
            tcprcvbuf          1204       9576    2383107    5659907          0
            othersockbuf      20896      29268    1191553    4468353          0
            dgramrcvbuf           0       2228    1191553    1191553          0
            numothersock         24         30        800        800          0
            dcachesize       322624     332280    3704295    3815424          0
            numfile             719        777       6624       6624          0
            dummy                 0          0          0          0          0
            dummy                 0          0          0          0          0
            dummy                 0          0          0          0          0
            numiptent            10         10        200        200          0

Are these values correct and expedient? What does the value "2147483647" at VMGUARPAGES mean?
2147483647 memory pages are roughly 8192 Gigabytes, is this the maximal allocatable memory size of OpenVZ?

Thanks.

[Updated on: Sun, 19 February 2006 10:49]

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Re: Memory Management again [message #25109 is a reply to message #1668]

Fri, 14 December 2007 14:50

Sten
Messages: 5
Registered: December 2007

Junior Member

„Guaranteed“ (barrier) means any application in the VE can use the memory, „burst“ (limit) is the very maximum value of memory taken; memory between barrier and limit can be used by applications running under root only.

2147483647 is the maximal value of 32-bit unsigned integer, so if you’re running 32-bit system, it’s the maximum allocable memory of the OpenVZ.

xor rsi,rsi
lodsb
Segmentation fault

E-mail returned to sender â€“ Insufficient voltage

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Re: Memory Management again [message #25604 is a reply to message #1668]

Thu, 03 January 2008 03:19

ledude1
Messages: 9
Registered: December 2007

Junior Member

Atomic and Sten.

This is awesome example on how to calculate the memory and memory burst. I've been trying my dearest to understand exactly what this one means reading the manual and for some reason this one answer my question.

But I have one more question though and perhaps someone can help me understand it.

PRIVVMPAGES="256000:262140"	// 1024MB Burst

I know it is for the memory burst but help me understand again how I do the calculation?
I understand that the 256000 is where you get the 1024 Mb burst but what's 262140? What's that mean on the bean counter by limit? Is it basically means that you can have range or memory burst from 1024 to 1048? Please help me understand it? I've read the manual and it makes no sense to me. Also how do I get the 262140?

Many thanks for all of your help and pardon me being a nooby. Smile

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Re: Memory Management again [message #25605 is a reply to message #25604]

Thu, 03 January 2008 07:30

vaverin
Messages: 708
Registered: September 2005

Senior Member

I hope you will find answers on your questions here:
http://wiki.openvz.org/Privvmpages#privvmpages

thank you,
Vasily Averin

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Re: Memory Management again [message #25618 is a reply to message #1668]

Thu, 03 January 2008 16:00

ledude1
Messages: 9
Registered: December 2007

Junior Member

Thanks Vasily.

It kind of explains it except that it didn't go into details on how it comes up with the 262140. Is there like a best practice number on how to obtain the number.

PRIVVMPAGES="256000:262140"	// 1024MB Burst

Many thanks for taking your guys time to explain this number. Razz

[Updated on: Thu, 03 January 2008 16:01]

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Re: Memory Management again [message #25676 is a reply to message #1668]

Mon, 07 January 2008 04:27

ledude1
Messages: 9
Registered: December 2007

Junior Member

#bump...

Anyone?

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Re: Memory Management again [message #25688 is a reply to message #25618]

Mon, 07 January 2008 12:18

ugob
Messages: 271
Registered: March 2007

Senior Member

It looks like they use a 1000:1024 ratio. This is probably just an arbitrary way to get human-readable parameters and give 'a little more' to the hard limit.

Please read the manual before asking questions:
http://download.openvz.org/doc/OpenVZ-Users-Guide.pdf

Please have a look at the wiki before asking questions:
http://wiki.openvz.org/Main_Page

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Re: Memory Management again [message #25704 is a reply to message #25688]

Mon, 07 January 2008 20:03

ledude1
Messages: 9
Registered: December 2007

Junior Member

Thanks Ugob.

I guess there's really no special number calculation that needs to be perform to get the number other than using the ratio you mentioned earlier. Very interesting. Confused

Thanks again Ugob. Cool

Anyone else want to chime in? Very Happy

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Re: Memory Management again [message #25714 is a reply to message #25704]

Tue, 08 January 2008 06:49

vaverin
Messages: 708
Registered: September 2005

Senior Member

http://wiki.openvz.org/Privvmpages#privvmpages:
"There should be a safety gap between the barrier and the limit for privvmpages parameter to reduce the number of memory allocation failures that the application is unable to handle. This gap will be used for “high-priority” memory allocations, such as process stack expansion. Normal priority allocations will fail when the barrier if privvmpages is reached."

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Re: Memory Management again [message #25768 is a reply to message #1668]

Tue, 08 January 2008 18:40

ledude1
Messages: 9
Registered: December 2007

Junior Member

Thanks Vasily.

What I'm missing is that how it ended up using the ratio 1000:1024 to obtain this number? Like I said earlier, i've read the manual but nowhere in it that stated a mathematical formula on how to get this number. 256000:262140.

But thanks again anyway. Smile

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Re: Memory Management again [message #25800 is a reply to message #25768]

Wed, 09 January 2008 08:42

vaverin
Messages: 708
Registered: September 2005

Senior Member

In vzsplit utility we use 10% gap for privvmpages limit. However there is not any strong recommedation about this delta and you can use some % or just have some constant value for it.

thank you,
Vasily Averin

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