linux-kernel - Re: [PATCH 2/9] mm: alloc_contig_freed

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Message-ID: <op.v3j6y8i33l0zgt@mpn-glaptop>
Date:	Tue, 18 Oct 2011 11:00:34 -0700
From:	"Michal Nazarewicz" <mina86@...a86.com>
To:	"Dave Hansen" <dave@...ux.vnet.ibm.com>
Cc:	"Marek Szyprowski" <m.szyprowski@...sung.com>,
	"Mel Gorman" <mel@....ul.ie>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org,
	linux-mm@...ck.org, linaro-mm-sig@...ts.linaro.org,
	"Kyungmin Park" <kyungmin.park@...sung.com>,
	"Russell King" <linux@....linux.org.uk>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
	"Ankita Garg" <ankita@...ibm.com>,
	"Daniel Walker" <dwalker@...eaurora.org>,
	"Arnd Bergmann" <arnd@...db.de>,
	"Jesse Barker" <jesse.barker@...aro.org>,
	"Jonathan Corbet" <corbet@....net>,
	"Shariq Hasnain" <shariq.hasnain@...aro.org>,
	"Chunsang Jeong" <chunsang.jeong@...aro.org>
Subject: Re: [PATCH 2/9] mm: alloc_contig_freed_pages() added

On Tue, 18 Oct 2011 10:48:46 -0700, Dave Hansen <dave@...ux.vnet.ibm.com> wrote:

> On Tue, 2011-10-18 at 10:26 -0700, Michal Nazarewicz wrote:
>> > You can do this in a more general fashion by checking the
>> > zone boundaries and resolving the pfn->page every MAX_ORDER_NR_PAGES.
>> > That will not be SPARSEMEM specific.
>>
>> I've tried doing stuff that way but it ended up with much more code.
>
> I guess instead of:
>
>>> +static inline bool zone_pfn_same_memmap(unsigned long pfn1, unsigned long pfn2)
>>> +{
>>> +    return pfn_to_section_nr(pfn1) == pfn_to_section_nr(pfn2);
>>> +}
>
> You could do:
>
> static inline bool zone_pfn_same_maxorder(unsigned long pfn1, unsigned long pfn2)
> {
> 	unsigned long mask = MAX_ORDER_NR_PAGES-1;
> 	return (pfn1 & mask) == (pfn2 & mask);
> }
>
> I think that works.  Should be the same code you have now, basically.

Makes sense.  It'd require calling pfn_to_page() every MAX_ORDER_NR_PAGES even
in memory models that have linear mapping of struct page, but I guess that's
not that bad.

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +----<email/xmpp: mpn@...gle.com>--------------ooO--(_)--Ooo--
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