On Mon, 16 Jul 2001, Rik van Riel wrote:

On Mon, 16 Jul 2001, Kanoj Sarcar wrote:

quoted

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.

Yes, the system ended up swapping as soon as the first zone
was filled up and after that would fill up the other zones;
the way the system stabilised was cycling through the pages
of one zone and leaving the lower zones alone.

This reduced the amount of available VM of a 1GB system
to 128MB, which is somewhat suboptimal ;)

What we learned from that is that we need to have some
way to auto-balance the reclaiming, keeping the objective
of evicting the least used page from RAM in mind.

quoted

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,

quoted

try_to_swap_out is a good example, which can be solved
by rmaps.

Indeed. Most of the time things go right, but the current
system cannot cope at all when things go wrong. I think we
really want things like rmaps and more sturdy reclaiming
mechanisms to cope with these worst cases (and also to make
the common case easier to get right).

As I said to Kanoj, I agree that we really want rmaps to fix that thing
right.

Now I don't see any other way for fixing that on _2.4_ except something
similar to the patch I posted. That patch can still have problems in
practice, but fundamentally _it is the right thing_, IMO.


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