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Weird memory numbers [message #20194]

Thu, 13 September 2007 08:03

dagr
Messages: 83
Registered: February 2006

Member

I made expirement to understand whether i can see how much memory exactly my vps consumes

I installed apache and run it with 100 start processes (prefork mpm model)


[[email]root@vps-10811[/email] conf]# ps -eo "sz,size,rss,vsize,pid,cmd" | grep httpd| wc -l
102                                                                 

[[email]root@vps-10811[/email] conf]# ps -eo "sz,size,rss,vsize,pid,cmd" | grep httpd 
 1451 1244 2520 5804 30193 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2136 5936 32109 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2136 5936 32110 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2136 5936 32111 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2140 5936 32112 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2140 5936 32113 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2140 5936 32114 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2140 5936 32115 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2140 5936 32116 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2140 5936 32117 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2144 5936 32118 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2140 5936 32119 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2140 5936 32120 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2140 5936 32121 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2140 5936 32122 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2140 5936 32123 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2140 5936 32124 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2140 5936 32125 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2140 5936 32126 /vps_core/apache-2.2.3/bin/httpd -k start   
 1484 1376 2140 5936 32127 /vps_core/apache-2.2.3/bin/httpd -k start   
.................
 1451 1244 1720 5804 32217 /vps_core/apache-2.2.3/bin/httpd -k start
 1451 1244 1720 5804 32219 /vps_core/apache-2.2.3/bin/httpd -k start
 395 160 520 1580  5144 grep httpd

ps shows memory usage in tricky way , so i checked it by pmap

[[email]root@vps-10811[/email] conf]# pmap -d 32217
.........................

mapped: 5808K    writeable/private: 1428K    shared: 48K

writeable/private: 1428K - is the minimum memory which process uses and doesnt share.
Its close to size 1451K from ps in our case . Ie 100x1458 = 150 Mb

Now lets see what beancounters give us

[[email]root@vps-10811[/email] conf]# cat /proc/user_beancounters                              
Version: 2.5                                                                    
       uid  resource           held    maxheld    barrier      limit    failcnt 
     10811: kmemsize       11638464   13987632   20752512   29036012          0 
            lockedpages           0          0         32         32          0 
            privvmpages       24687      27632     600000     700000          0 
            shmpages            652        661     249152     249152          0 
            dummy                 0          0          0          0          0 
            numproc             110        119        200        200          0 
            physpages          7099       7854          0 2147483647          0 
            vmguarpages           0          0      60000 2147483647          0 
            oomguarpages       7099       7854      60000 2147483647          0 
            numtcpsock            6        174        300        300          0 
            numflock              3          4        100        110          0 
            numpty                1          1         16         16          0 
            numsiginfo            0        101        256        256          0 
            tcpsndbuf         51428     206412    1319488    2524288          0 
            tcprcvbuf         84888     942160    1319488    2524288          0 
            othersockbuf       2236       9800    5036896    5536896          0 
            dgramrcvbuf           0      13980     232096     500000          0 
            numothersock          4          9        100        100          0 
            dcachesize            0          0    1800000    2000000          0 
            numfile            1087       1398       4048       4048          0 
            dummy                 0          0          0          0          0

Both privvmpages (~100Mb) and oomguarpages(~28Mb) show me numbers far from expected. Im pretty sure about pmap method , so whats the trick ?

( 2.6.9-023stab044.4-enterprise , vzctl-3.0.13-1 )

[Updated on: Thu, 13 September 2007 08:05]

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Re: Weird memory numbers [message #20196 is a reply to message #20194]

Thu, 13 September 2007 08:17

dev
Messages: 1693
Registered: September 2005
Location: Moscow

Senior Member

taking a look at pmap: AFAICS it scans /proc/<pid>/maps file, which is not enough in reallity to tell how much RAM is used.

Look, read-only mappings are consuming memory as well.
glibc, executable etc. all these goes to UBC::oomguarpages and in pmap::Mapped. So taking into account only "Writeable/Private" is wrong.

http://static.openvz.org/userbars/openvz-developer.png

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Re: Weird memory numbers [message #20197 is a reply to message #20196]

Thu, 13 September 2007 08:21

dagr
Messages: 83
Registered: February 2006

Member

I mot taking ONLY. I said that at least it must be private/writable size. it means at least 150Mb . Not ?

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Re: Weird memory numbers [message #20198 is a reply to message #20197]

Thu, 13 September 2007 08:51

dev
Messages: 1693
Registered: September 2005
Location: Moscow

Senior Member

1. I don't remember whether mpm model implies all threads or all processes or mixed. It depends very much on this.
so please add to your ps output pid and tgid plz.

2. plus plz add full output of pmap -d, since I can't see what regions are used.

3. oomguarpages are much lower then "writeable/private"*100, since many of these writeable areas are not fully touched/used and all the writeable areas from libraries can be shared between the processes until modified. So *100 is a very high estimation. oomguarpages shows real page usages.

4. So the only thing to understand left: why privvmpages << "writeable/private" * 100, correct?

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Re: Weird memory numbers [message #20203 is a reply to message #20198]

Thu, 13 September 2007 09:21

dagr
Messages: 83
Registered: February 2006

Member

4. So the only thing to understand left: why privvmpages << "writeable/private" * 100, correct?

Yes

1. MPM prefork implies simple forking just like in Apache 1.3 - no threads at all.
tgid - you mean gid ?

[root@vps-10811 extra]# ps -eo "sz,size,rss,vsize,pid,gid,ppid,cmd" | grep httpd
                                                                                
 1452 1248 2488 5808 25791   0     1 /vps_core/apache-2.2.3/bin/httpd -k start  
 1485 1380 1704 5940 30233   2 25791 /vps_core/apache-2.2.3/bin/httpd -k start  
 1485 1380 1700 5940 30234   2 25791 /vps_core/apache-2.2.3/bin/httpd -k start

group 2 - daemon

2.

[root@vps-10811 extra]# pmap -d 30233                                    
30233:   /vps_core/apache-2.2.3/bin/httpd -k start                       
Address   Kbytes Mode  Offset           Device    Mapping                
00111000      56 r-x-- 0000000000000000 007:0000f libpthread-2.3.4.so    
0011f000       4 r---- 000000000000d000 007:0000f libpthread-2.3.4.so    
00120000       4 rw--- 000000000000e000 007:0000f libpthread-2.3.4.so    
00121000       8 rw--- 0000000000121000 000:00000   [ anon ]             
00123000      76 r-x-- 0000000000000000 007:0000f libgssapi_krb5.so.2.2  
00136000       4 rw--- 0000000000013000 007:0000f libgssapi_krb5.so.2.2  
00137000      60 r-x-- 0000000000000000 007:0000f libresolv-2.3.4.so     
00146000       4 r---- 000000000000f000 007:0000f libresolv-2.3.4.so     
00147000       4 rw--- 0000000000010000 007:0000f libresolv-2.3.4.so     
00148000       8 rw--- 0000000000148000 000:00000   [ anon ]             
001fc000      36 r-x-- 0000000000000000 007:0000f libnss_files-2.3.4.so  
00205000       4 r---- 0000000000008000 007:0000f libnss_files-2.3.4.so  
00206000       4 rw--- 0000000000009000 007:0000f libnss_files-2.3.4.so  
00229000       8 r-x-- 0000000000000000 007:0000f libuuid.so.1.2         
0022b000       4 rw--- 0000000000001000 007:0000f libuuid.so.1.2         
002c5000      60 r-x-- 0000000000000000 007:0000f libz.so.1.2.1.2        
002d4000       4 rw--- 000000000000e000 007:0000f libz.so.1.2.1.2        
002f5000      76 r-x-- 0000000000000000 0fd:00000 libaprutil-1.so.0.2.7  
00308000       4 rw--- 0000000000012000 0fd:00000 libaprutil-1.so.0.2.7  
00319000      84 r-x-- 0000000000000000 007:0000f ld-2.3.4.so            
0032e000       4 r---- 0000000000015000 007:0000f ld-2.3.4.so            
0032f000       4 rw--- 0000000000016000 007:0000f ld-2.3.4.so         
00349000     100 r-x-- 0000000000000000 0fd:00000 libexpat.so.0.1.0   
00362000       8 rw--- 0000000000019000 0fd:00000 libexpat.so.0.1.0   
00385000     124 r-x-- 0000000000000000 0fd:00000 libapr-1.so.0.2.7   
003a4000       4 rw--- 000000000001f000 0fd:00000 libapr-1.so.0.2.7   
003a9000     132 r-x-- 0000000000000000 007:0000f libm-2.3.4.so       
003ca000       4 r---- 0000000000020000 007:0000f libm-2.3.4.so       
003cb000       4 rw--- 0000000000021000 007:0000f libm-2.3.4.so       
003e9000      32 r-x-- 0000000000000000 007:0000f librt-2.3.4.so      
003f1000       4 r---- 0000000000007000 007:0000f librt-2.3.4.so      
003f2000       4 rw--- 0000000000008000 007:0000f librt-2.3.4.so      
003f3000      40 rw--- 00000000003f3000 000:00000   [ anon ]          
00475000     196 r-x-- 0000000000000000 007:0000f libssl.so.0.9.7a    
004a6000      12 rw--- 0000000000031000 007:0000f libssl.so.0.9.7a    
004a9000    1172 r-x-- 0000000000000000 007:0000f libc-2.3.4.so       
005ce000       8 r---- 0000000000124000 007:0000f libc-2.3.4.so       
005d0000       8 rw--- 0000000000126000 007:0000f libc-2.3.4.so       
005d2000       8 rw--- 00000000005d2000 000:00000   [ anon ]          
0097f000     128 r-x-- 0000000000000000 007:0000f libk5crypto.so.3.0  
0099f000       4 rw--- 0000000000020000 007:0000f libk5crypto.so.3.0  
009a3000     396 r-x-- 0000000000000000 007:0000f libkrb5.so.3.2      
00a06000       8 rw--- 0000000000063000 007:0000f libkrb5.so.3.2      
00b87000       8 r-x-- 0000000000000000 007:0000f libcom_err.so.2.1   
00b89000       4 rw--- 0000000000001000 007:0000f libcom_err.so.2.1   
00bf4000       8 r-x-- 0000000000000000 007:0000f libdl-2.3.4.so      
00bf6000       4 r---- 0000000000001000 007:0000f libdl-2.3.4.so        
00bf7000       4 rw--- 0000000000002000 007:0000f libdl-2.3.4.so        
00cf1000     848 r-x-- 0000000000000000 007:0000f libcrypto.so.0.9.7a   
00dc5000      72 rw--- 00000000000d4000 007:0000f libcrypto.so.0.9.7a   
00dd7000      12 rw--- 0000000000dd7000 000:00000   [ anon ]            
00f15000      20 r-x-- 0000000000000000 007:0000f libcrypt-2.3.4.so     
00f1a000       4 r---- 0000000000004000 007:0000f libcrypt-2.3.4.so     
00f1b000       4 rw--- 0000000000005000 007:0000f libcrypt-2.3.4.so     
00f1c000     156 rw--- 0000000000f1c000 000:00000   [ anon ]            
08048000     668 r-x-- 0000000000000000 0fd:00000 httpd                 
080ef000      16 rw--- 00000000000a6000 0fd:00000 httpd                 
080f3000      20 rw--- 00000000080f3000 000:00000   [ anon ]            
09520000    1080 rw--- 0000000009520000 000:00000   [ anon ]            
b7fc2000      48 rw-s- 0000000000000000 000:00033   [ anon ]            
b7fce000      20 rw--- 00000000b7fce000 000:00000   [ anon ]            
bfff7000      28 rw--- 00000000bfff7000 000:00000   [ stack ]           
ffffe000       4 ----- 0000000000000000 000:00000   [ anon ]            
mapped: 5944K    writeable/private: 1564K    shared: 48K

3. So you say that real consumption is oomguarpages. May be oomguarpages << privmpages when processes idle or processing same document - in other words, in docs you call privmpages some kind of memusage prediction. So in what case apache will consume privmpages which i see now?

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Re: Weird memory numbers [message #20205 is a reply to message #20203]

Thu, 13 September 2007 09:32

dev
Messages: 1693
Registered: September 2005
Location: Moscow

Senior Member

1. let's honestly sum up all pmap info from all the processes. multiplication by 100 can be not honest.

2.
> So you say that real consumption is oomguarpages. May be
> oomguarpages << privmpages when processes idle or processing same
> document - in other words, in docs you call privmpages some kind
> of memusage prediction. So in what case apache will consume
> privmpages which i see now?

for any normal application privvmapes is around 20-50% of oomguarpages. it is normal, since apps never touch all the memory they map.
however, in special case or in maliscuios apps all the memory counted to privvmpages can be really allocated and thus oomguarpages can be equal to privvmpages.

yes, oomguarpages is current real usage of physical pages + swap pages.

privvmpages is a high estimation of what can be allocated by application w/o denials.

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Re: Weird memory numbers [message #20213 is a reply to message #20205]

Thu, 13 September 2007 11:07

dagr
Messages: 83
Registered: February 2006

Member

[root@vps-10811 extra]# s=0;n=0;for pid in ` ps -ef | grep httpd  | grep -v "gre
p"| awk '{print $2}'`;do                                                        
>  a=`pmap -d $pid | grep private | awk '{print $4}'`;                          
>  l=`expr length $a - 1`;                                                      
>  b=`expr substr $a 1 $l`                                                      
>  s=`expr $s + $b`                                                             
>  n=`expr $n + 1 `                                                             
> done                                                                          
[root@vps-10811 extra]# echo "s=$s"                                             
s=157832                                                                        
[root@vps-10811 extra]# echo "num=$n"                                           
num=101

2. I cant understand this.
"it is normal, since apps never touch all the memory they map"
But OS cant know for sure that app wont touch it later , so it must ne isolated ie - busy, and other app cant use it same time . In this terms i dont understand sense of 2 parameters like oom and priv, should be only 1. Example above is simple. I need to estimate how much processes my apache can run and nothing more, ie i should take overall memory and divide by lets say 1.5 Mb.

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Re: Weird memory numbers [message #20215 is a reply to message #20213]

Thu, 13 September 2007 11:24

dev
Messages: 1693
Registered: September 2005
Location: Moscow

Senior Member

1. hmm... strange
I'll check

2. No. OS doesn't know in reallity how much RAM you will consume.
Look, you can mmap 1GB private mappings on machine with 100Mb of RAM. You will be allowed to do so on std kernel (without disabled overcimmitment). i.e. this 1GB will be charged to privvmpages.
The real memory pages are allocated later when application really wants to touch the memory. This is what charged to oomguarpages.

Applications very often map files privately with write access, so potentially they can have a full private copy of file in memory. But in reallity they touch only small pieces of it, so little memory is required. And that's why privvmpages >> oomguarpages.

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Re: Weird memory numbers [message #20503 is a reply to message #20194]

Wed, 19 September 2007 10:03

xemul
Messages: 248
Registered: November 2005

Senior Member

Please, check with "ps -o pid,tid,comm" that all the http processes are not threads (I didn't notice whether you did this).

If they are threads, then the answer is: pmap can't handle this at all.

Otherwise, could you please create a tarball with this VE and let us download it?

Thanks,
Pavel

[Updated on: Wed, 19 September 2007 10:03]

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Re: Weird memory numbers [message #20510 is a reply to message #20503]

Wed, 19 September 2007 12:39

dagr
Messages: 83
Registered: February 2006

Member

Its not threads

[root@vps-10811 conf]# ps -eo "pid,tid,comm"  
  PID   TID COMMAND                           
    1     1 init                              
31992 31992 syslogd                           
32002 32002 sshd                              
32013 32013 httpd                             
32028 32028 crond                             
32035 32035 httpd                             
32036 32036 httpd                             
32037 32037 httpd                             
32038 32038 httpd                             
32039 32039 httpd                             
32040 32040 httpd                             
32041 32041 httpd                             
32042 32042 httpd                             
32043 32043 httpd                             
32044 32044 httpd                             
32045 32045 httpd                             
32046 32046 httpd                             
32047 32047 httpd                             
32048 32048 httpd                             
32049 32049 httpd                             
32050 32050 httpd                             
32051 32051 httpd                             
32052 32052 httpd     
...........                        


[root@vps-10811 conf]# httpd -l | grep prefork 
  prefork.c

I checked situation on another HN - its the same

VE can be downloaded here

http://209.3.12.11/d/10811.img.tgz

(confs,private dir and loopback_ro_image)

(apache starts automatically after VE start)

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Re: Weird memory numbers [message #20588 is a reply to message #20194]

Fri, 21 September 2007 11:43

xemul
Messages: 248
Registered: November 2005

Senior Member

Well, I've got it Smile

The answer is - this is normal. Point is that httpd uses private readonly mappings. Reading from these regions results in so called ZERO_PAGE appears in the address space. ZERO_PAGE is a reserved 4k chunk of memory which is used only for this or similar purposes. We do not account for this page, since it doesn't increase the RSS at all, but its presence is "accounted" with the pmap utility.

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Re: Weird memory numbers [message #20606 is a reply to message #20588]

Sat, 22 September 2007 15:54

dagr
Messages: 83
Registered: February 2006

Member

Cool , and the last question .

When do i really need to take into account privvmpages ?
So far it looks more like inner technical parameter.

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Re: Weird memory numbers [message #20620 is a reply to message #20606]

Mon, 24 September 2007 07:03

dev
Messages: 1693
Registered: September 2005
Location: Moscow

Senior Member

you need to take it into account when limiting your VE.
plz note that physpages limit doesn't affect VE.
and oomguarpages is a gurantee, not a limit.
So privvmpages is the only handle to control VE memory.

P.S. In future we'll add physpages limiting leading to VE swap-out, but this is not efficient way of control memory, since swap bandwidth is scarce resource.

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