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: <20150428145632.GN2449@suse.de>
Date:	Tue, 28 Apr 2015 15:56:32 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
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, Apr 28, 2015 at 06:48:10AM -0700, Andrew Morton wrote:
> 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.
> 

Take 2. Suggestions on different names are welcome because they are poor.

/*
 * Deferred struct page initialisation requires init functions that are freed
 * before kswapd is available. Reuse the memory hotplug section annotation
 * to mark the required code.
 *
 * __defermem_init is code that always exists but is annotated __meminit to
 *      avoid section warnings.
 * __defer_init code gets marked __meminit when deferring struct page
 *      initialistion but is otherwise in the init section.
 */


-- 
Mel Gorman
SUSE Labs
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