Hi,

Thanks to the help of some knowledgeable people(here and elsewhere), I managed to succusfully set up a server.

Unfortunately, whenever I import a large file using apache/php/mysql, it gets stuck in the RAM. For some reason, its never flushed.

So my question is this: Is there a command to flush the RAM of stuff thats not doing anything? Or a program maybe?

-Thanks

I'm not a memory allocation expert, but I'm fairly certain that flushing out unused RAM is the kernel's job; it's something that should happen automatically.

How do you know your imported file is "stuck" in RAM? What does the output of 'free' (run from the command-line) show?

UNIX kernels aggressively cache things in RAM. It's not uncommon to have 99% of your RAM filled, even when idle.

That's a good thing. What is the point of having free RAM, it doesn't speed you up at all? It's there to be used, so the OS should efficiently use it.

So fear not, the kernel can handle memory management. ;-)

I too thought that job belonged to linux. Can you make out anything from the information below?


09:26:34 up 4:40, 2 users, load average: 0.09, 0.11, 0.03

53 processes: 52 sleeping, 1 running, 0 zombie, 0 stopped

CPU states: 0.0% user 0.3% system 0.0% nice 0.0% iowait 99.6% idle
Mem: 385824k av, 245576k used, 140248k free, 0k shrd, 35836k buff
99668k active, 128664k inactive

Swap: 610428k av, 12144k used, 598284k free 171876k cached



PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME CPU COMMAND
2062 root 12 0 1524 1480 1320 S 0.1 0.3 0:00 0 sshd
2076 root 14 0 1024 1024 816 R 0.1 0.2 0:00 0 top
1 root 8 0 76 68 52 S 0.0 0.0 0:05 0 init
2 root 8 0 0 0 0 SW 0.0 0.0 0:00 0 keventd
3 root 18 19 0 0 0 SWN 0.0 0.0 0:00 0 ksoftirqd_CPU
4 root 9 0 0 0 0 SW 0.0 0.0 0:00 0 kswapd
5 root 9 0 0 0 0 SW 0.0 0.0 0:00 0 bdflush
6 root 9 0 0 0 0 SW 0.0 0.0 0:00 0 kupdated
10 root -1 -20 0 0 0 SW< 0.0 0.0 0:00 0 mdrecoveryd
11 root 9 0 0 0 0 SW 0.0 0.0 0:00 0 kreiserfsd
136 root 9 0 0 0 0 SW 0.0 0.0 0:00 0 eth0
166 root 9 0 0 0 0 SW 0.0 0.0 0:00 0 khubd
809 root 9 0 608 588 528 S 0.0 0.1 0:00 0 syslogd
812 root 9 0 440 388 388 S 0.0 0.1 0:00 0 klogd
815 root 9 0 520 464 464 S 0.0 0.1 0:00 0 inetd
818 root 9 0 1088 972 884 S 0.0 0.2 0:00 0 sshd

woops! posted that before I saw your reply. Thanks. that makes perfect sense.

So if a task needs memory, an idle one will be terminated?

No, it will simple remove un-needed information from ram or write to swap. Should you run out of ram + swap, then I think the most memory hogging process is killed. (This can be configured further in 2.6.x I believe)

hey, ive got another question, so if the ram is filled, and linux starts writing to the swap, what if our swap is a whole heck of a lot slower, and I would much rather have it write to the ram.

Im asking this because my ram gets filled up, and then it starts writing to my swap, but my swap is an old piece of crap hard drive i stuck in there for extra storage, so does it put the new processes in the ram and move old ones to swap? Or does it just write the new processes to anything thats open?

New ones go to RAM, then, as a process is brought to the foreground, it's taken from swap and put into RAM, and one from RAM is put into SWAP

is that true for both windows and *nix? IIRC that is how windows handels swap too, just not as effective as *nix at keeping things were it belongs.

AFAIK that's how its done in both. I do know though, that win makes mistakes a lot and "forgets" to move something into RAM and out of the paging file before trying to execute it. But, in essence, they're supposed to work roughly the same.