linux-kernel - Re: [PATCH] Tight check of pfn_valid on sparsemem

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Message-ID: <AANLkTimtN9PuvwrB2PAUZMajWzg=TbEP1jeseVM3MST3@mail.gmail.com>
Date:	Sun, 25 Jul 2010 22:33:08 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>,
	Johannes Weiner <hannes@...xchg.org>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH] Tight check of pfn_valid on sparsemem - v3

On Sun, Jul 25, 2010 at 7:32 PM, Minchan Kim <minchan.kim@...il.com> wrote:
> Changelog since v2
>  o Change some function names
>  o Remove mark_memmap_hole in memmap bring up
>  o Change CONFIG_SPARSEMEM with CONFIG_ARCH_HAS_HOLES_MEMORYMODEL
>
> I have a plan following as after this patch is acked.
>
> TODO:
> 1) expand pfn_valid to FALTMEM in ARM
> I think we can enhance pfn_valid of FLATMEM in ARM.
> Now it is doing binary search and it's expesive.
> First of all, After we merge this patch, I expand it to FALTMEM of ARM.
>
> 2) remove memmap_valid_within
> We can remove memmap_valid_within by strict pfn_valid's tight check.
>
> 3) Optimize hole check in sparsemem
> In case of spasemem, we can optimize pfn_valid through defining new flag
> like SECTION_HAS_HOLE of hole mem_section.
>

Is there an assumption somewhere that assumes that page->private will
always have MEMMAP_HOLE set when the pfn is invalid, independent of
the context in which it is invoked? BTW, I'd also recommend moving
over to using set_page_private() and page_private() wrappers (makes
the code easier to search)

Balbir
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