linux-kernel - Re: [patch 4/6] mm: merge populate and nopage into fault (fixes nonlinear)

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Message-ID: <20070307071909.GI18774@holomorphy.com>
Date:	Tue, 6 Mar 2007 23:19:09 -0800
From:	Bill Irwin <bill.irwin@...cle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Nick Piggin <npiggin@...e.de>,
	Linux Memory Management <linux-mm@...ck.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch 4/6] mm: merge populate and nopage into fault (fixes nonlinear)

On Tue, Mar 06, 2007 at 10:51:01PM -0800, Andrew Morton wrote:
> Does anybody really pass a NULL `type' arg into filemap_nopage()?

The major vs. minor fault accounting patch that introduced the argument
didn't make non-NULL type arguments a requirement. It's essentially an
optional second return value and the NULL pointer represents the caller
choosing to ignore it. I'm not sure I actually liked that aspect of it,
but that's how it ended up going in. I think it had something to do
with driver churn clashing with the sweep at the time of the merge. I'd
rather the argument be mandatory and defaulted to VM_FAULT_MINOR.

It's something of a non-answer, though, since it only discusses a
convention as opposed to reviewing specific callers of filemap_nopage().
NULL type arguments to ->nopage() are rare at most, and could be easily
eliminated, at least for in-tree drivers.

egrep -nr 'nopage.*NULL' . 2>/dev/null | grep -v '^Bin' on a current
git tree yields zero matches.

-- wli
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