Hi Eli... > I've got a couple nodes (running inside VM on a s390) that are using > up every bit of there swap, yet only using a 1/3 to 1/2 there memory > (-buffers/cache). Geez, you have s390? Can you give me a free SSH account? :) I heard virtualization on s390 is ancient but one of the best in the world :) > Here is free -m from a node: > $ free -m > total used free shared buffers > cached Mem: 1008 1002 5 0 98 > 514 -/+ buffers/cache: 390 618 > Swap: 99 93 6 Hm, so actually page cache is around 98+514= 612 MB. Quite big, but surely it helps relieving I/O pressure in some cases... > So out of 1008MB total memory we're only using 390, Not to bad. But > it does seem kinda bad when you look at it as you have 514MB in cache > but your almost out of swap. well, usually people allocate swap bigger than the available RAM, but this rule is somewhat "informal"... > This leads to my 2 questions. > 1 Why am i using any swap when i have so much memory free? (and is > that a problem, if so would adding more memory even help? How about > more swap?) Actually, from kernel point of view, you have low free RAM. Somehow you need to make the kernel dedicate lesser portion of RAM for page cache. Too bad I can't find one, but the closest I can find is /proc/sys/vm/vfs_cache_pressure. read Documentation/filesystems/proc.txt for further explanations. > 2 How do i tell whats in swap anyway. like a lot of memory management > stuff there doesn't seem to be a easy way to tell. Possibly it contains lots of swapped-out anonymous pages. For fun, try something like: strings -t x /dev/<your swap device> | head -30 and see in case you see your shell history there :) regards Mulyadi -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
