TOURNIER Frédéric wrote:
Heres my benches, done in two days so dates are weird and results are very approximative.
What surprises me are in the Part 2, swap occured.
I don't know exactly why, but I have seen a small usage of swap
occasionally without real memory pressure. So I'd consider this normal.
In 3 and 4, the ram is eaten up, even if the vm just booted.
Where is the RAM eaten up? I see always always 800 MB free, some more
even after the d/l:
You have to look at the second line of the free column, no the first
one. As you can see the OS has still enough RAM to afford a large cache,
so it uses this. Unused RAM is just a waste of resources (because it is
always there and there is no reason to not use it). If the 'cached'
contains a lot of clean pages, the OS can simply claim them should an
application request more memory. If you want a proof of this, try:
# echo 3 > /proc/sys/vm/drop_caches
This should free the cache and give you a high "real" free value back.
Have you tried cache=none with the tmpfs scenario? That should save you
some of the host's cached memory (note the difference between part 1 and
part2 in that respect), maybe at the expense of the guest's memory used
more heavily. Your choice here, that depends on the actual memory
utilization in the guest.
As I said before, it is not a very good idea to use such a setup (with
the relative image on tmpfs) if you are doing actual disk I/O,
especially large writes. AFAIK QCOW[2] does not really shrink, it only
grows, so you will end up with out-of-memory at some point.
But if you can restrict the amount of written data, this may work.
Regards,
Andre.
P.S. Sorry for the confusion about tmpfs vs. ramfs in my last week's mail.
------------------------------------
Part 0
End of boot :
bash-3.1$ free
total used free shared buffers cached
Mem: 2056840 500836 1556004 0 2244 359504
-/+ buffers/cache: 139088 1917752
Swap: 3903784 0 3903784
------------------------------------
Part 1
qemu-system-x86_64 -m 1024 -vga std -usb -usbdevice tablet -localtime -soundhw es1370 -name qlio -drive file=/mnt/hd/sda/sda1/tmp/relqlio.img,cache=none
bash-3.1$ free
total used free shared buffers cached
Mem: 2056840 1656280 400560 0 34884 378332
-/+ buffers/cache: 1243064 813776
Swap: 3903784 0 3903784
bash-3.1$ ls -lsa /mnt/hd/sda/sda1/tmp/relqlio.img
58946 -rw-r--r-- 1 ftournier info 60424192 2010-09-16 17:49 /mnt/hd/sda/sda1/tmp/relqlio.img
650M download inside the vm
bash-3.1$ free
total used free shared buffers cached
Mem: 2056840 1677648 379192 0 33860 397716
-/+ buffers/cache: 1246072 810768
Swap: 3903784 0 3903784
bash-3.1$ ls -lsa /mnt/hd/sda/sda1/tmp/relqlio.img
914564 -rw-r--r-- 1 ftournier info 935723008 2010-09-20 14:07 /mnt/hd/sda/sda1/tmp/relqlio.img
------------------------------------
Part 2
reboot
qemu-system-x86_64 -m 1024 -vga std -usb -usbdevice tablet -localtime -soundhw es1370 -name qlio -drive file=/mnt/hd/sda/sda1/tmp/relqlio.img
bash-3.1$ free
total used free shared buffers cached
Mem: 2056840 2040172 16668 0 32952 758948
-/+ buffers/cache: 1248272 808568
Swap: 3903784 0 3903784
bash-3.1$ ls -lsa /mnt/hd/sda/sda1/tmp/relqlio.img
60739 -rw-r--r-- 1 ftournier info 62259200 2010-09-16 17:57 /mnt/hd/sda/sda1/tmp/relqlio.img
650M download inside the vm
bash-3.1$ free
total used free shared buffers cached
Mem: 2056840 2040540 16300 0 34412 765208
-/+ buffers/cache: 1240920 815920
Swap: 3903784 8160 3895624
bash-3.1$ ls -lsa /mnt/hd/sda/sda1/tmp/relqlio.img
842430 -rw-r--r-- 1 ftournier info 861929472 2010-09-20 14:20 /mnt/hd/sda/sda1/tmp/relqlio.img
------------------------------------
Part 3
reboot
qemu-system-x86_64 -m 1024 -vga std -usb -usbdevice tablet -localtime -soundhw es1370 -name qlio -drive file=/tmp/relqlio.img
note : /tmp is a tmpfs filesystem
bash-3.1$ free
total used free shared buffers cached
Mem: 2056840 2009688 47152 0 248 766328
-/+ buffers/cache: 1243112 813728
Swap: 3903784 0 3903784
bash-3.1$ ls -lsa /tmp/relqlio.img
59848 -rw-r--r-- 1 ftournier info 61407232 2010-09-16 18:04 /tmp/relqlio.img
650M download inside the vm
bash-3.1$ free
total used free shared buffers cached
Mem: 2056840 2041404 15436 0 128 921276
-/+ buffers/cache: 1120000 936840
Swap: 3903784 248804 3654980
bash-3.1$ ls -lsa /tmp/relqlio.img
885448 -rw-r--r-- 1 ftournier info 906821632 2010-09-20 14:40 /tmp/relqlio.img
------------------------------------
Part 4
reboot
qemu-system-x86_64 -m 1024 -vga std -usb -usbdevice tablet -localtime -soundhw es1370 -name qlio -drive file=/dev/shm/relqlio.img
bash-3.1$ free
total used free shared buffers cached
Mem: 2056840 2009980 46860 0 172 767328
-/+ buffers/cache: 1242480 814360
Swap: 3903784 0 3903784
bash-3.1$ ls -lsa /dev/shm/relqlio.img
58496 -rw-r--r-- 1 ftournier info 59899904 2010-09-16 18:11 /dev/shm/relqlio.img
650M download inside the vm
bash-3.1$ free
total used free shared buffers cached
Mem: 2056840 2041576 15264 0 92 938976
-/+ buffers/cache: 1102508 954332
Swap: 3903784 266232 3637552
bash-3.1$ ls -lsa /dev/shm/relqlio.img
1016912 -rw-r--r-- 1 ftournier info 1039400960 2010-09-20 15:15 /dev/shm/relqlio.img
--
Andre Przywara
AMD-OSRC (Dresden)
Tel: x29712
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