Chuck Swiger a écrit :
On Oct 28, 2008, at 9:49 AM, Francis Dubé wrote:
Here's an example of top's output regarding our httpd process :
54326 apache 1 96 0 156M 13108K select 1 0:00 0.15%
httpd
54952 apache 1 96 0 156M 12684K select 1 0:00 0.10%
httpd
52343 apache 1 4 0 155M 12280K select 0 0:01 0.10%
httpd
Most of our page are in HTML with a LOT of images. Few PHP pages,
very light PHP processing.
156M x 450 process = way more RAM than what we have (same for
RES). Concretely, how must I interpret these results?
First, your Apache children are huge, at least for FreeBSD. :-)
Also, they are mostly paged out, which suggests your system is under
significant VM pressure, but the vmstat output would be helpful to
confirm.
I'll try to remove some useless modules.
Here's the output of vmstat, i should've pasted it in the previous
message, sorry about that.
vmstat -s
3777275311 cpu context switches
2105577673 device interrupts
359873900 software interrupts
2670696893 traps
2635245695 system calls
43 kernel threads created
42717777 fork() calls
824925 vfork() calls
0 rfork() calls
5130 swap pager pageins
7513 swap pager pages paged in
5266 swap pager pageouts
10722 swap pager pages paged out
518980 vnode pager pageins
1659001 vnode pager pages paged in
5717865 vnode pager pageouts
11193440 vnode pager pages paged out
5530 page daemon wakeups
140578661 pages examined by the page daemon
1701262 pages reactivated
2968698933 copy-on-write faults
3856240 copy-on-write optimized faults
4090371353 zero fill pages zeroed
3851399420 zero fill pages prezeroed
457318 intransit blocking page faults
1628587285 total VM faults taken
0 pages affected by kernel thread creation
3234876655 pages affected by fork()
88075637 pages affected by vfork()
0 pages affected by rfork()
1591911567 pages freed
2 pages freed by daemon
4139768534 pages freed by exiting processes
331854 pages active
367993 pages inactive
41103 pages in VM cache
118472 pages wired down
93794 pages free
4096 bytes per page
125580578352 total name lookups
cache hits (98% pos + 0% neg) system 0% per-directory
deletions 0%, falsehits 0%, toolong 0%
It's as I expected -- you don't understand the difference between
SIZE (SZ) and RES (RSS). The simple version:
SIZE == amount of memory that's shared across all processes on the
machine, e.g. shared libraries. It doesn't mean "156MB is being taken
up per process".
SIZE == the amount of VM address space allocated by the process.
It includes things shared (copy-on-write) between many processes like
the shared libraries; it also includes memory-mapped files (including
.so's like apache modules being loaded into the process), VM allocated
but not yet used by malloc()/brk(), the stack, and so forth.
RES == amount of memory that's specifically allocated to that
individual
process. The three httpd processes above are taking up a total of
~38MBytes of memory (13108K + 12684K + 12280K).
RES == the amount of process VM that is resident in actual physical
RAM; the rest of the process is paged out to the swapfile or
filesystem for memory-mapped files.
As I said, even with RES the numbers dont seems to have any sense.
Let's say 12500K x 450 = ~5500MBytes. Considering there's a lot of
process other than Apache running on the server...there's something
wrong. Is there something shared in RES too ?
Yep. Quite probably a lot, but the amount of memory which is specific
to just that process is not easily found from FreeBSD's top, regrettably.
For the sake of example, and because the same explanation applies
pretty closly to FreeBSD, consider an httpd running on a MacOSX
system. Here's top output, which includes columns "RPRVT" for
"resident memory used by just this process", "RSHRD" which is
"resident, shared with other processes", "RSIZE" which is FreeBSD's
"RES", and "VSIZE", which is FreeBSD's "SIZE":
Processes: 136 total, 4 running, 132 sleeping... 215 threads
11:06:40
Load Avg: 1.71, 1.66, 1.62 CPU usage: 12.5% user, 59.7% sys,
27.8% idle
SharedLibs: num = 141, resident = 18.3M code, 2.92M data, 6.40M LinkEdit
MemRegions: num = 10360, resident = 101M + 5.91M private, 159M shared
PhysMem: 159M wired, 252M active, 99.0M inactive, 510M used, 1.50G
free
VM: 7.16G + 88.8M 1378510(0) pageins, 88743(0) pageouts
PID COMMAND %CPU TIME #TH #PRTS #MREGS RPRVT RSHRD RSIZE
VSIZE
2868 httpd 0.0% 43:21.28 1 12 92 1.82M 144M
72.9M 169M
2869 httpd 0.0% 46:29.45 1 12 92 1.95M 144M
73.2M 169M
2870 httpd 0.0% 46:55.84 1 12 92 1.89M 144M
73.0M 169M
...and the vmmap command, documented here:
http://developer.apple.com/documentation/Darwin/Reference/ManPages/man1/vmmap.1.html
...provides detailed info about a single process' VM usage:
# vmmap 2870
Virtual Memory Map of process 2870 (httpd)
Output report format: 2.0
==== Non-writable regions for process 2870
__PAGEZERO 00000000-00001000 [ 4K] ---/--- SM=NUL
/usr/sbin/httpd
__TEXT 00001000-00050000 [ 316K] r-x/rwx SM=COW
/usr/sbin/httpd
__LINKEDIT 0005a000-00065000 [ 44K] r--/rwx SM=COW
/usr/sbin/httpd
__TEXT 00065000-00068000 [ 12K] r-x/rwx SM=COW
/usr/libexec/httpd/mod_log_config.so
__LINKEDIT 00069000-0006a000 [ 4K] r--/rwx SM=COW
/usr/libexec/httpd/mod_log_config.so
__TEXT 0006a000-0006c000 [ 8K] r-x/rwx SM=COW
/usr/libexec/httpd/mod_mime.so
__LINKEDIT 0006d000-0006e000 [ 4K] r--/rwx SM=COW
/usr/libexec/httpd/mod_mime.so
[ ... ]
__DATA a1a0e000-a1a20000 [ 72K] r--/r-- SM=COW
/usr/lib/libcrypto.0.9.7.dylib
__DATA a1a20000-a1a23000 [ 12K] r--/r-- SM=COW
/usr/lib/libcrypto.0.9.7.dylib
__DATA a4f2c000-a4f2f000 [ 12K] r--/r-- SM=COW
/usr/lib/libssl.0.9.7.dylib
__DATA a7233000-a7235000 [ 8K] r--/r-- SM=NUL
/System/Library/Perl/lib/5.8/libperl.dylib
system fffec000-fffef000 [ 12K] ---/rwx SM=NUL
commpage [libobjc.A.dylib]
system fffef000-ffff0000 [ 4K] r-x/rwx SM=COW
commpage [libobjc.A.dylib]
system ffff8000-ffffa000 [ 8K] r--/r-- SM=SHM
commpage [libSystem.B.dylib]
==== Writable regions for process 2870
__DATA 00050000-00059000 [ 36K] rw-/rwx SM=COW
/usr/sbin/httpd
__DATA 00059000-0005a000 [ 4K] rw-/rwx SM=COW
/usr/sbin/httpd
__DATA 00068000-00069000 [ 4K] rw-/rwx SM=COW
/usr/libexec/httpd/mod_log_config.so
__DATA 0006c000-0006d000 [ 4K] rw-/rwx SM=COW
/usr/libexec/httpd/mod_mime.so
[ ... ]
__DATA a0a3a000-a0a4f000 [ 84K] rw-/rw- SM=COW
/usr/lib/libobjc.A.dylib
__OBJC a0a4f000-a0a50000 [ 4K] rw-/rw- SM=COW
/usr/lib/libobjc.A.dylib
__DATA a0b70000-a0b71000 [ 4K] rw-/rw- SM=COW
/usr/lib/libauto.dylib
__DATA a1425000-a1426000 [ 4K] rw-/rw- SM=COW
/usr/lib/libgcc_s.1.dylib
__DATA a7229000-a7233000 [ 40K] rw-/rw- SM=COW
/System/Library/Perl/lib/5.8/libperl.dylib
Stack bf800000-c0000000 [ 8192K] rw-/rwx SM=COW
thread 0
==== Legend
SM=sharing mode:
COW=copy_on_write PRV=private NUL=empty ALI=aliased
SHM=shared ZER=zero_filled S/A=shared_alias
==== Summary for process 2870
ReadOnly portion of Libraries: Total=18840KB resident=10976KB(58%)
swapped_out_or_unallocated=7864KB(42%)
Writable regions: Total=51100KB written=548KB(1%)
resident=27276KB(53%) swapped_out=0KB(0%) unallocated=23824KB(47%)
REGION TYPE [ VIRTUAL]
=========== [ =======]
MALLOC [ 42400K]
Stack [ 8192K]
VM_ALLOCATE ? [ 364K]
__DATA [ 1048K]
__LINKEDIT [ 4352K]
__OBJC [ 4K]
__PAGEZERO [ 4K]
__TEXT [ 14488K]
mapped file [ 120368K]
shared memory [ 4K]
system [ 24K]
Note that you can obtain somewhat similar information under FreeBSD
using the sysutils/pmap port:
PID USERNAME THR PRI NICE SIZE RES STATE TIME WCPU
COMMAND
40037 www 1 4 0 28820K 11532K accept 1:10 0.00%
httpd
# pmap 40037
40037: /usr/local/sbin/httpd
Address Kbytes RSS Shared Priv Mode Mapped File
08048000 280 208 280 - r-x /usr/local/sbin/httpd
0808E000 8 8 - 8 rw- /usr/local/sbin/httpd
08090000 16 - - - rw- [swap pager]
08094000 976 - - - rwx [swap pager]
08188000 2420 - - - rwx [swap pager]
083E5000 6968 - - - rwx [swap pager]
2808E000 144 92 144 - r-x /libexec/ld-elf.so.1
280B2000 8 4 8 - rw- /libexec/ld-elf.so.1
280B4000 20 - - - rw- [swap pager]
280B9000 32 - - - rwx [swap pager]
280C1000 64 16 64 - r-x /lib/libz.so.3
[ ... ]
2920F000 4 0 4 - r-x
/usr/local/lib/php/20060613/dom.so
29210000 16 0 16 - rwx
/usr/local/lib/php/20060613/dom.so
29214000 60 - - - rwx [swap pager]
29225000 16 - - - rwx [swap pager]
BFBE0000 128 - - - rwx [swap pager]
-------- ------- ------- ------- -------
Total Kb 28740 3996 17384 456
...and the pmap manpage talks about how to understand this:
" To calculate the amount of memory a group of processes is using:
- for each process of the same binary, count the private
memory
used for n-1 processes.
- for each binary, count the total resident size once.
For example, using the pmap data above, we can calculate that 20
bash
binaries would used
452Kbytes * 19 + 1416Kbytes = 8588 + 1416 Kbytes
= 8588Kbytes"
Regards,
Thanks for the explanation and for the tool, i've installed it. Now my
numbers makes more sense :)
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