Re: [PATCH] ignore referenced pages on reclaim when OOM

[Marcelo Tosatti <marcelo.tosatti@cyclades.com>]

On Wed, Nov 10, 2004 at 02:29:00PM -0800, Andrew Morton wrote:
> Marcelo Tosatti <marcelo.tosatti@cyclades.com> wrote:
> >
> > So z->all_unreclaimable logic and "OOM detection" are conflicting goals.
> 
> Only in a single case: where a zone is all_unreclaimable and some pages
> have recently become reclaimable but we don't know about it yet.

The thing is - if you dont scan the zones "enough" you have no way of 
reliably knowing it is OOM.

But on the other hand, scanning it wastes CPU time - what you call "mad scanning".

They are two extremes, I feel we need a balance between them.

> Certainly it can happen, but it sounds really unlikely to me.  So I suspect
> that if you were to fix that problem by some means, it wouldn't help
> anything.
> 
>But maybe I'm wrong, or maybe the all_unreclaimable logic has rotted. 

I dont think all_unreclaimable logic is rotted - it does what what it is
expected to do. 

At least thats how I see things, maybe I'm wrong and it is indeed rotted.

> Have you tried simply disabling it?

Tried now - if I disable it then balance_pgdat() detects the OOM situation by noticing
its not successful freeing pages (thus setting worked_dma and worked_normal, 
see patch), and kills the memory hog. Side note, the memory hog runs _much_ faster
without all_unreclaimable logic.

I'll continue hacking on this tomorrow.

As always, thanks for the input :D

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