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

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

quoted

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

quoted

quoted

patches to Linus for in the 2.3.43 time frame or

so.

quoted

quoted

I think later performance work ripped out that

work.

quoted

Yes, the system ended up swapping as soon as the

first zone

quoted

was filled up and after that would fill up the

other zones;

quoted

the way the system stabilised was cycling through

the pages

quoted

of one zone and leaving the lower zones alone.

This reduced the amount of available VM of a 1GB

system

quoted

to 128MB, which is somewhat suboptimal ;)

What we learned from that is that we need to have

some

quoted

way to auto-balance the reclaiming, keeping the

objective

quoted

of evicting the least used page from RAM in mind.

quoted

I guess the problem is that a lot of the

different

quoted

quoted

page reclamation schemes first of all do not

know

quoted

quoted

how to reclaim pages for a specific zone,

quoted

try_to_swap_out is a good example, which can be

solved

quoted

quoted

by rmaps.

Indeed. Most of the time things go right, but the

current

quoted

system cannot cope at all when things go wrong. I

think we

quoted

really want things like rmaps and more sturdy

reclaiming

quoted

mechanisms to cope with these worst cases (and

also to make

quoted

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.

Yes, I agree with you, and that is why I had sent the
patch to Linus during 2.3 in the first place.  

What I am trying to point out is that you should talk
to Rik, and understand why it was removed previously.
Rik  obviously had his reasons at that point, but some
of those might not apply anymore, given that 2.4 is
quite different from 2.3.43.

Kanoj
 

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