linux-kernel - Re: [ltt-dev] [PATCH] Fix dirty page accounting in redirty_page_for

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Date:	Fri, 1 May 2009 15:31:11 -0400 (EDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Yuriy Lalym <ylalym@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	ltt-dev@...ts.casi.polymtl.ca, Tejun Heo <tj@...nel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [ltt-dev] [PATCH] Fix dirty page accounting in
 redirty_page_for_writepage()

On Fri, 1 May 2009, Mathieu Desnoyers wrote:

> What I do here is to let those u8 counters increment as free-running
> counters. Yes, they will periodically overflow the 8 bits. But I don't
> rely on this for counting the number of increments we need between
> global counter updates : I use the bitmask taken from the threshold
> value (which is now required to be a power of two) to detect 0, 1, 2, 3,
> 4, 5, 6 or 7-bit counter overflow. Therefore we can still have the kind
> of granularity currently provided. The only limitation is that we have
> to use powers of two for the threshold, so we end up counting in power
> of two modulo, which will be unaffected by the u8 overflow.

Ack. Got it. Looks good.

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