Re: Free memory level in 2.6.16?

Andi Kleen
2006-10-05T20:02:04Z

Steve Bergman <sbergman@rueb.com> writes:

> Due to some problems I was having with the CentOS4.4 kernel, I just
> moved a box (x86 with 4GB ram) to 2.6.16.29 from kernel.org.
>
> All is well, but I am curious about one thing. This is a fairly memory
> hungry box, serving about 40 gnome desktops via xdmcp. All VM settings
> are at the default. Swappiness=60, min_free_kbytes=3831.
>
> However, it seems to seek out about 150MB for the level of free memory
> that it maintains. Typically I see somewhere between 100MB an 500MB in
> swap, buffers+cache is about 500MB, and 150MB is free.
>
> If I cat from /dev/md0 to /dev/null, the free memory does go down, to
> 25MB or so, but then I can watch as it seeks out about 150MB of free
> memory.
>
> To me, free memory is wasted memory. Is this a bug or a feature?

Normally it keeps some memory free for interrupt handlers which
cannot free other memory. But 150MB is indeed a lot, especially
it's only in the ~900MB lowmem zone.

You could play with /proc/sys/vm/lowmem_reserve_ratio but must
likely some defaults need tweaking.

-Andi