linux-kernel - Re: [PATCH 0/6] PM / Hibernate: Memory bitmap scalability improvements

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Date:	Mon, 21 Jul 2014 16:39:05 +0200
From:	Pavel Machek <pavel@....cz>
To:	Joerg Roedel <joro@...tes.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6] PM / Hibernate: Memory bitmap scalability
 improvements

On Mon 2014-07-21 16:29:51, Joerg Roedel wrote:
> Hi,
> 
> On Mon, Jul 21, 2014 at 01:45:07PM +0200, Pavel Machek wrote:
> > Ok, so you have sped it up from O(n) to O(log(n)) speed, and increased
> > memory requirements from O(n) to O(n * log(n)), right?
> 
> No, new memory requirements are still ~O(n), because the additional pages
> needed for the index in the radix tree are outweighted by the memory
> saved by the smaller size of struct rtree_node compared to struct
> bm_block.

Are we in agreement how O() notation works?

So you reduced O(n) to O(n/2 log(n)) ... that's still O(n log(n)), right?

> You can also modify the above tool to give you some data to plot, then
> you will also SEE that there is still a linear relationship between RAM
> size and memory required by the old and new memory bitmap
> implementation.

I believe radix tree is O(log(N)) per operation, but its memory is
certainly not linear.

Yes, log(n) is looks quite constant even for huge n :-).
									Pavel
-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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