| How is the privvmpages limit reached? [message #27101] |
Sat, 09 February 2008 12:45  |
Wheel
Messages: 3
Registered: February 2008
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Junior Member |
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I trying to run Java (memory allocation intensive) on a VPS, and getting privvmpages limit problems.
I know that increasing privvmpages limit, using Xen, or decreasing the Java XMX usage, will fix the problem. But I'm wondering why and how Java reaches this privvmpages limit.
I have two VPSes:
XEN VPS:
-256mb guaranteed
-512mb swap
-No memory problems
[root@vps proc]#ps -aux --sort -vsize
Warning: bad syntax, perhaps a bogus '-'? See /usr/share/doc/procps-3.2.7/FAQ
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
tomcat 18099 0.2 26.9 236172 70580 ? Sl Feb08 3:39 jsvc.exec -user tomcat -home /usr/java/default -Dcatalina.home=/opt/tomcat -Dcatalina.base=/opt/
tomcat 23131 27.7 16.9 222084 44592 pts/2 Sl+ 10:19 0:09 /usr/java/default/bin/java -classpath /usr/share/java/ant.jar:/usr/share/java/ant-launcher.jar:/
tomcat 23091 25.4 17.0 221920 44692 pts/0 Sl+ 10:19 0:09 /usr/java/default/bin/java -classpath /usr/share/java/ant.jar:/usr/share/java/ant-launcher.jar:/
tomcat 23306 56.9 16.7 220756 44052 pts/1 Sl+ 10:19 0:08 /usr/java/default/bin/java -classpath /usr/share/java/ant.jar:/usr/share/java/ant-launcher.jar:/
mysql 18071 0.4 12.3 147652 32312 ? Sl Feb08 6:30 /usr/libexec/mysqld --defaults-file=/etc/my.cnf --basedir=/usr --datadir=/var/lib/mysql --user=m
............
[root@vps proc]#free
total used free shared buffers cached
Mem: 262312 259472 2840 0 1216 35272
-/+ buffers/cache: 222984 39328
Swap: 525304 2772 522532
OpenVZ VPS:
-384MB guaranteerd
- ~800MB privvmpages/burst?
-Memory problems when using the same apps as the XEN vps.
[root@vps ]# ant -f build-run-linux.xml
Error occurred during initialization of VM
Could not reserve enough space for code cache
[root@vps proc]# ps -aux --sort -vsize
Warning: bad syntax, perhaps a bogus '-'? See /usr/share/doc/procps-3.2.7/FAQ
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
tomcat 17460 0.3 6.1 203984 48340 ? Sl 01:44 0:06 jsvc.exec -user tomcat -home /usr/java/default -Dcatalina.home=/opt/tomcat -Dcatalina.base=/opt/tomcat -Djava.io.tmpdir=/var/tmp -w
root 23818 71.3 5.0 193520 39484 pts/1 Sl+ 02:14 0:04 /usr/java/latest/jre/bin/java -classpath /usr/share/ant/lib/ant-launcher.jar -Dant.home=/usr/share/ant -Dant.library.dir=/usr/share
root 23808 56.0 5.0 193348 40052 pts/0 Sl+ 02:14 0:04 /usr/java/latest/jre/bin/java -classpath /usr/share/ant/lib/ant-launcher.jar -Dant.home=/usr/share/ant -Dant.library.dir=/usr/share
mysql 16196 0.1 3.8 143256 30148 pts/0 Sl 01:41 0:02 /usr/libexec/mysqld --defaults-file=/etc/my.cnf --basedir=/usr --datadir=/var/lib/mysql --user=mysql --pid-file=/var/run/mysqld/mys
.......
[root@vps proc]# cat user_beancounters
Version: 2.5
uid resource held maxheld barrier limit failcnt
982850: kmemsize 7287695 7764715 2147483646 2147483646 0
lockedpages 0 0 999999 999999 0
privvmpages 188389 191204 196608 196608 3
shmpages 3885 3901 98304 98304 0
dummy 0 0 0 0 0
numproc 109 113 999999 999999 0
physpages 40864 43050 0 2147483647 0
vmguarpages 0 0 98304 2147483647 0
oomguarpages 40864 43050 98304 2147483647 0
numtcpsock 62 67 7999992 7999992 0
numflock 6 11 999999 999999 0
numpty 4 4 500000 500000 0
numsiginfo 0 2 999999 999999 0
tcpsndbuf 1292928 1334288 80530432 262556672 0
tcprcvbuf 1249536 1371040 80530432 262556672 0
othersockbuf 13920 32896 80530432 262556672 0
dgramrcvbuf 0 8464 80530432 262556672 0
numothersock 18 24 7999992 7999992 0
dcachesize 0 0 2147483646 2147483646 0
numfile 2571 2638 23999976 23999976 0
dummy 0 0 0 0 0
dummy 0 0 0 0 0
dummy 0 0 0 0 0
numiptent 14 14 999999 999999 0
[root@vps proc]# free
total used free shared buffers cached
Mem: 786432 755120 31312 0 0 0
-/+ buffers/cache: 755120 31312
Swap: 0 0 0
As can be seen above, the XEN vps with less memory than the OpenVZ vps, did not cause any memory probems, while the OpenVZ vps with more total (inc burst) memory did cause memory problems by hitting privvmpages.
I read on a number of different sites that hitting privvmpages is caused by OpenVZ showing the total ammount of RAM on the hardware machine/Host instead of the amount of RAM on the VPS.
Someone said to me "OpenVZ does offer SLM like propoerties in reporting RAM so you should be ok with day to day usage of it rather than the old method where is reported the RAM of the host".
And the "free" command also shows a total RAM of the VPS and not that of the host.
My question is:
1) Why is the OpenVZ having memory problems while it has more memory than the Xen VPS?
2) Is the statement correct that Java sees [as total ram] the amount of the VPS (~800mb) and not that of the host?
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| Re: How is the privvmpages limit reached? [message #27104 is a reply to message #27101] |
Sat, 09 February 2008 16:48  |
rickb
Messages: 368
Registered: October 2006
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Senior Member |
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Hi, it sounds like you have been reading webhostingtalk for technical information. not a good idea.. 
jre is known for allocating _far_ more memory then it needs. due to this, your privvmpages will be much higher then physpages. other applications such as bind exhibit this as well. this is why you will never see privvmpages.limit=vmguarpages.limit
@@@
privvm=188389
phys=40864
In this case, your apps are allocating X amounts of memory and using X/4 to store data in it. There is no way to correct this in openvz; you should provide an adequate privvmpages limit for your application's hunger. Privvmpages is not a "burst" memory in the true sense, as your applications cannot realistically store 196608 pages (your limit) of data in memory. but, a high privvmpages on a non overcommitted hardware node can allow overuse of your vmguarpages.limit, which is a memory burst. the amount of burstable memory is difficult to report, rather you can report the memory allocation burst. the non vz linux kernel allows you to allocate as much memory as you wish, which is why your xen environment does not have this problem.
| Quote: |
Someone said to me "OpenVZ does offer SLM like propoerties in reporting RAM so you should be ok with day to day usage of it rather than the old method where is reported the RAM of the host"
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there are 2 sources for memory reporting- proc/meminfo and proc/user_beancounters. the most accurate source is always user_beancounters.
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And the "free" command also shows a total RAM of the VPS and not that of the host
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read the vzctl man page for the 'meminfo' option; it is possible to customize proc/meminfo reporting.
Cheers
Rick
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Common Terms I post with: http://wiki.openvz.org/Category:Definitions
UBC. Learn it, love it, live it: http://wiki.openvz.org/Proc/user_beancounters
[Updated on: Sun, 10 February 2008 02:57] Report message to a moderator |
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| Re: How is the privvmpages limit reached? [message #27116 is a reply to message #27101] |
Sun, 10 February 2008 01:58 |
Wheel
Messages: 3
Registered: February 2008
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Junior Member |
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Hi,
Thank you for your reply.
I read your post, but I do yet not fully understand why the Xen vps doesn't have memory problems.
(Correct me if I'm wrong.)
On the XEN vps it is able to allocate at most 768mb (guaranteed+swap). And on the OpenVZ vps it is able to allocate at least 403mb (98304 vmguarpages barrier) and at most 805mb (196608 privvmpages barrier).
To me it looks like the OpenVZ did not yet reach the privvmpages barrier, (since has a higher privvmpages barrier than the unfailed Xen VPS), but it did fail.
The doc says:
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If the current amount of allocated memory space exceeds the guarantee but below the barrier of privvmpages, allocations may or may not succeed, depending on the total amount of available memory in the system.
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So can I conclude that the OpenVZ space has too little available memory in the hardware node? Or might there also be another reason?
[Updated on: Sun, 10 February 2008 01:58] Report message to a moderator |
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| Re: How is the privvmpages limit reached? [message #27117 is a reply to message #27116] |
Sun, 10 February 2008 03:00 |
rickb
Messages: 368
Registered: October 2006
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Senior Member |
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You do not see this problem on xen for the same reason you do not see it on a stock linux kernel.
http://www.redhat.com/magazine/001nov04/features/vm/
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overcommit_memory is a value which sets the general kernel policy toward granting memory allocations. If the value is 0, then the kernel checks to determine if there is enough memory free to grant a memory request to a malloc call from an application. If there is enough memory, then the request is granted. Otherwise, it is denied and an error code is returned to the application. If the setting in this file is 1, the kernel allows all memory allocations, regardless of the current memory allocation state. If the value is set to 2, then the kernel grants allocations above the amount of physical RAM and swap in the system as defined by the overcommit_ratio value. Enabling this feature can be somewhat helpful in environments which allocate large amounts of memory expecting worst case scenarios but do not use it all.
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http://www.gnu.org/software/gnusound/Documentation/ar01s05.h tml
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Memory overcommit is a Linux kernel feature that lets applications allocate more memory than is actually available. The idea behind this feature is that some applications allocate large amounts of memory "just in case", but never actually use it. Thus, memory overcommit allows you to run more applications than actually fit in your memory, provided the applications don't actually use the memory they've allocated. If they do, then the kernel terminates the application.
GNUsound needs enough memory (RAM + swap) to load a file into memory completely. GNUsound will try to recover gracefully from memory allocation failures, but sometimes it simply can't. In particular, you may have problems when using a kernel that has memory overcommit enabled. This may result in GNUsound being killed as it tries to load the file. To try and solve the problem, you can either increase the amount of memory (by adding RAM or swap), or you can disable memory overcommit by typing (as root):
$ echo 2 > /proc/sys/vm/overcommit_memory
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Common Terms I post with: http://wiki.openvz.org/Category:Definitions
UBC. Learn it, love it, live it: http://wiki.openvz.org/Proc/user_beancounters
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