linux-kernel - Re: [patch 1/2] mm: change dirty limit type specifiers to unsigned long

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Message-ID: <alpine.DEB.2.00.0811241140390.19930@chino.kir.corp.google.com>
Date:	Mon, 24 Nov 2008 11:49:00 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Chinner <david@...morbit.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/2] mm: change dirty limit type specifiers to unsigned
 long

On Mon, 24 Nov 2008, Peter Zijlstra wrote:

> This didn't pop up any weird and wonderfull assumptions on the
> signed-ness of these variables I take it :-)
> 

It didn't; in fact, callers already used them as though they were 
unsigned.  For example, bdi_debug_stats_show():

	seq_printf(m,
		   "BdiDirtyThresh:   %8lu kB\n"
		   "DirtyThresh:      %8lu kB\n"
		   "BackgroundThresh: %8lu kB\n",
		   K(bdi_thresh),
		   K(dirty_thresh),
		   K(background_thresh));

And get_dirty_limits() itself implicitly uses an unsigned type specifier 
for the long *pbdi_dirty limit:

	if (bdi) {
		u64 bdi_dirty;
		...
		*pbdi_dirty = bdi_dirty;
	}

And, given that the remainder of the get_dirty_limits() callers simply use 
these for comparisons to the ZVC global_page_state() values, which are 
also unsigned long, this conversion is safe.

Thanks Peter!
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