linux-kernel - Re: [PATCH 07/13] mm: meminit: Initialise a subset of struct pages if CONFIG_DEFERRED_STRUCT_PAGE

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Message-Id: <20150428064810.0882ad36.akpm@linux-foundation.org>
Date:	Tue, 28 Apr 2015 06:48:10 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linux-MM <linux-mm@...ck.org>, Nathan Zimmer <nzimmer@....com>,
	Dave Hansen <dave.hansen@...el.com>,
	Waiman Long <waiman.long@...com>,
	Scott Norton <scott.norton@...com>,
	Daniel J Blueman <daniel@...ascale.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 07/13] mm: meminit: Initialise a subset of struct pages
 if CONFIG_DEFERRED_STRUCT_PAGE_INIT is set

On Tue, 28 Apr 2015 10:53:23 +0100 Mel Gorman <mgorman@...e.de> wrote:

> > > +#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
> > > +#define __defermem_init __meminit
> > > +#define __defer_init    __meminit
> > > +#else
> > > +#define __defermem_init
> > > +#define __defer_init __init
> > > +#endif
> > 
> > Could we get some comments describing these?  What they do, when and
> > where they should be used.  I have a suspicion that the naming isn't
> > good, but I didn't spend a lot of time reverse-engineering the
> > intent...
> > 
> 
> Of course. The next version will have
> 
> +/*
> + * Deferred struct page initialisation requires some early init functions that
> + * are removed before kswapd is up and running. The feature depends on memory
> + * hotplug so put the data and code required by deferred initialisation into 
> + * the __meminit section where they are preserved.
> + */

I'm still not getting it even a little bit :(  You say "data and code",
so I'd expect to see

#define __defer_meminitdata __meminitdata
#define __defer_meminit __meminit

But the patch doesn't mention the data segment at all.

The patch uses both __defermem_init and __defer_init to tag functions
(ie: text) and I can't work out why.

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