linux-kernel - Re: [PATCH 1/8] badpage: simplify page

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Date:	Tue, 2 Dec 2008 14:12:05 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Russ Anderson <rja@....com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Dave Jones <davej@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/8] badpage: simplify page_alloc flag check+clear

On Tue, 2 Dec 2008, Christoph Lameter wrote:
> On Tue, 2 Dec 2008, Hugh Dickins wrote:
> 
> > > But they are always clear on free. The checking is irrelevant.
> >
> > How about CHECK_PAGE_FLAGS_CLEAR_AT_FREE?
> 
> Strange name.

Looks like I'm not going to be able to satisfy you then.  I didn't
introduce the names in the patch, so let's leave them as is for now,
and everybody can muse on what they should get called in the end.

> > > If (page->flags & (all the flags including dirty and SwapBacked))
> > > 	zap-em.
> >
> > That's exactly what I did, isn't it?
> 
> Yes but you added another instance of this.

Did I?  Whereabouts?  I wonder if you're thinking of the
+	page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
in prep_new_page(), which replaces the clearing of another
collection of flags which somehow didn't get named before.

That clearing is a temporary measure, to keep the handling
of PageReserved unchanged in that patch; then it vanishes in the
next patch, where we treat all bad_page candidates the same way.

> Can you consolidate all the check and clears into one?

You mean one test_and_clear_bits() that somehow covers the different
cases of what we expect at free time and what we need at alloc time?
I don't think so.

Hugh
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