On Mon, 20 Sep 2010 16:00:53 +0200 Andre Przywara <andre.przywara@xxxxxxx> wrote: > TOURNIER FrÃdÃric 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. Mmm i don't like strange normal things... Anyway my current setting is the NÂ1. And my target the 3 or 4 ^^. > > 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. Ok i'll take a closer look. But i see no reason why so much cache is used. I think there's some kind of "duplicated pages" between nfs and qemu-kvm. Maybe there's an idea for a future enhancement for some "-nfs-image" switch ? > Have you tried cache=none with the tmpfs scenario? Oh yeah i tried and tried. Unfortunately this is impossible : Invalid argument For shm and ramfs too. > 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. Well i'm aware of this "dangerous" setting but i really tried to make it work because it's so comfortable. If some of you readers have some spare time, and two machines (2G ram on each is a good start), try this setting. Read on NFS, write on local, ram if possible. The performance of the guest is awesome, especially if the original .img is pre-cached in the ram of the server. > > Regards, > Andre. > > P.S. Sorry for the confusion about tmpfs vs. ramfs in my last week's mail. No problem. Thank you for taking time. And beeing answered by someone@xxxxxxx is a must ^^ Fred. > > > > > ------------------------------------ > > 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 > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
