--- Marcelo Tosatti <marcelo@conectiva.com.br> wrote:

quoted

Hi,

As well known, the VM does not make a distiction
between global and
per-zone shortages when trying to free memory. That
means if only a given
memory zone is under shortage, the kernel will scan
pages from all zones. 

The following patch (against 2.4.6-ac2), changes the
kernel behaviour to
avoid freeing pages from zones which do not have an
inactive and/or
free shortage.

Now I'm able to run memory hogs allocating 4GB of
memory (on 4GB machine)
without getting real long hangs on my ssh session.
(which used to happen
on stock -ac2 due to exhaustion of DMA pages for
networking).

Comments ? 

Dirk, Can you please try the patch and tell us if it
fixes your problem ? 

Just a quick note. A per-zone page reclamation
method like this was what I had advocated and sent
patches to Linus for in the 2.3.43 time frame or so.
I think later performance work ripped out that work.
I guess the problem is that a lot of the different
page reclamation schemes first of all do not know
how to reclaim pages for a specific zone, and secondly
have to go thru a lot of work before they discover the
page they are trying to reclaim does not belong to the
shortage zone, hence wasting a lot of work/cputime.
try_to_swap_out is a good example, which can be solved
by rmaps.