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Date: Sun, 08 Sep 2002 14:51:04 -0700
From: Andrew Morton <akpm@digeo.com>
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To: Hugh Dickins <hugh@veritas.com>
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       William Lee Irwin III <wli@holomorphy.com>,
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Subject: Re: LMbench2.0 results
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Hugh Dickins wrote:
> 
> On Sun, 8 Sep 2002, Andrew Morton wrote:
> >
> > We need to find some way of making vm_enough_memory not call get_page_state
> > so often.  One way of doing that might be to make get_page_state dump
> > its latest result into a global copy, and make vm_enough_memory()
> > only get_page_state once per N invokations.  A speed/accuracy tradeoff there.
> 
> Accuracy is not very important in that sysctl_overcommit_memory 0 case
> e.g. the swapper_space.nr_pages addition was brought in at a time when
> it was very necessary, but usually overestimates now (or last time I
> thought about it).  The main thing to look out for is running the same
> memory grabber twice in quick succession: not nice if it succeeds the
> first time, but not the second, just because of some transient effect
> that its old pages are temporarily uncounted.
> 

That's right - there can be sudden and huge changes in pages used/free.

So any rate limiting tweak in there would have to be in terms of
number-of-pages rather than number-of-seconds.
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