Re: on load control / process swapping

[Jonathan Morton <chromi@cyberspace.org>]

>> FWIW, I've been running with a 2-line hack in my kernel for some weeks
>> now, which essentially forces the RSS of each process not to be forced
>> below some arbitrary "fair share" of the physical memory available.
>> It's not a very clean hack, but it improves performance by a very
>> large margin under a thrashing load.  The only problem I'm seeing is a
>> deadlock when I run out of VM completely, but I think that's a
>> separate issue that others are already working on.
>
>I'm pretty sure I know what you're running into.
>
>Say you guarantee a minimum of 3% of memory for each process;
>now when you have 30 processes running your memory is full and
>you cannot reclaim any pages when one of the processes runs
>into a page fault.

Actually I already thought of that one, and made it a "fair share" of the
system rather than a fixed amount.  IOW, the guaranteed amount is something
like (total_memory / nr_processes).  I think I was even sane enough to
lower this value slightly to allow for some buffer/cache memory, but I
didn't allow for locked pages (including the kernel itself).

The deadlock happened when the swap ran out, not the physical RAM, and is
independent of this particular hack - remember I'm running with some
out_of_memory() fixes and some other hackery I did a month or so ago
(remember that massive "OOM killer" thread?).  I should try to figure those
out and present cleaned-up versions for further perusal...

--------------------------------------------------------------
from:     Jonathan "Chromatix" Morton
mail:     chromi@cyberspace.org  (not for attachments)
big-mail: chromatix@penguinpowered.com
uni-mail: j.d.morton@lancaster.ac.uk

The key to knowledge is not to rely on people to teach you it.

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