On Mon, Feb 13, 2006 at 01:23:33PM -0500, Silbermann, Martine wrote:
> * From memory hotplug test plan to scripts - discussion
Here's some answers to questions that came up today.
1. What info is available from /proc/meminfo?
dev4-013 ~ # cat /proc/meminfo
MemTotal: 15919280 kB
MemFree: 10523152 kB
Buffers: 1300972 kB
Cached: 57528 kB
SwapCached: 0 kB
Active: 1136956 kB
Inactive: 229760 kB
HighTotal: 0 kB
HighFree: 0 kB
LowTotal: 15919280 kB
LowFree: 10523152 kB
SwapTotal: 508024 kB
SwapFree: 508024 kB
Dirty: 24 kB
Writeback: 0 kB
Mapped: 11628 kB
Slab: 4006412 kB
CommitLimit: 8467664 kB
Committed_AS: 22180 kB
PageTables: 356 kB
VmallocTotal: 2147483647 kB
VmallocUsed: 1128 kB
VmallocChunk: 2147482511 kB
HugePages_Total: 0
HugePages_Free: 0
Hugepagesize: 16384 kB
Here is a page defining what these parameters mean:
http://www.redhat.com/advice/tips/meminfo.html
2. How to determine what areas of memory a process is using?
I had remembered seeing a tool for this recently. After digging around
a bit I found it - it was an article I read a couple weeks ago that
explained the Linux memory model:
http://virtualthreads.blogspot.com/2006/02/understanding-memory-usage-on-linux.html
The command is `pmap`. You specify a process ID and it displays the
memory usage for that process and all of its libraries. For example:
aether /usr/src/linux (636)$ pmap 29415
29415: emacs -nw /tmp/mutt-aether-1000-22564-160
0000000000400000 1204K r-x-- /usr/bin/emacs.emacs-21
000000000062c000 4888K rw--- /usr/bin/emacs.emacs-21
0000000000af2000 284K rw--- [ anon ]
00002aaaaaaab000 84K r-x-- /lib64/ld-2.3.5.so
00002aaaaaac0000 188K rw--- [ anon ]
00002aaaaabbf000 4K r---- /lib64/ld-2.3.5.so
00002aaaaabc0000 4K rw--- /lib64/ld-2.3.5.so
00002aaaaabc1000 312K r-x-- /lib64/libncurses.so.5.4
......
That first column is the memory address. (I guess this is its virtual
memory address but I don't really know. The man page for pmap is pretty
anemic.)
Also, this looks interesting:
http://mail.nl.linux.org/linux-mm/2003-03/msg00077.html
3. How to enable/disable memory?
According to http://lhms.sourceforge.net/, this is done via:
# To boot a kernel with less than max memory, use the boot option "mem="
# and specify a smaller memory size than real.
# Identify new memory:
echo "(physical memory address)" > /sys/device/system/memory/probe
# Online memory
echo "online" > /sys/device/system/memory/memoryX/state
# Remove memory
echo "offline" > /sys/device/sysstem/memory/memoryX/state
I don't have a system with memory hotplug enabled presently, but I
notice that the above paths are incorrect at least in that it should be
/sys/devices/ not /sys/device/. Also, there's a typo in that last
command - /sysstem/ should be /system/.
4. How to control swapping
As a sysctl, the swappiness can be set at runtime with either of the
following commands:
sysctl -w vm.swappiness=30
echo 30 >/proc/sys/vm/swappiness
For more info see the 'Swappiness' section on this page:
http://gentoo-wiki.com/FAQ_Linux_Memory_Management
5. What tools may be affected by changes in memory?
Several tools off the top of my head:
top, sar, ps, top, free, vmstat, pmap
There's probably a lot more...
Bryce
