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Date: Fri, 12 Nov 1999 19:49:32 +0100 (CET)
From: Ingo Molnar <mingo@chiara.csoma.elte.hu>
To: "Stephen C. Tweedie" <sct@redhat.com>
Cc: Linus Torvalds <torvalds@transmeta.com>, linux-kernel@vger.rutgers.edu, Alan Cox <number6@the-village.bc.nu>
Subject: Re: [patch] zoned-2.3.27-E0
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On Fri, 12 Nov 1999, Stephen C. Tweedie wrote:

> > Stephen noticed that 2.3.27 doesnt boot on <=16MB boxes due to the zoned
> > allocator changes. The attached patch should fix this. Unfortunately i
> > found no way to prevent introducing the runtime 'nr_zones' variable.
> 
> A quick special-case check on zones known to be empty would allow you to
> maintain performance even if you have zones which will never have any
> pages in them on a given machine.

yes, i first did something like this, but it's just as slow in the end.
(well, there is just an academic slowdown anyway)

> You need this anyway --- Alan pointed out that it is a significant hit
> on benchmarks if, during normal running, one zone fills up and you
> start falling back routinely to a lower zone.

at that point we are wasting much more time already walking page tables in
kswapd and try_to_free_pages to free RAM.

and we'd have to get the spinlock to rely on zone->free_pages, and for any
non-page-sized allocation request zone->free_pages is not authorative.

-- mingo


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