From: Ralf Baechle <ralf@linux-mips.org>
To: zhuzhenhua <zzh.hust@gmail.com>
Cc: linux-mips <linux-mips@linux-mips.org>
Subject: Re: is remap_pfn_range should align to 2(n) * (page size) ?
Date: Fri, 9 May 2008 10:56:05 +0100 [thread overview]
Message-ID: <20080509095605.GB14450@linux-mips.org> (raw)
In-Reply-To: <50c9a2250805082354x1edc1ecar89dcc3378b3bbe75@mail.gmail.com>
On Fri, May 09, 2008 at 02:54:29PM +0800, zhuzhenhua wrote:
> i have a sensor driver want to malloc 2.xM SDRAM to capture
> data(using DMA), so i used remap_pfn_range to malloc 3M.
> But in /proc/meminfo, it showes free memory reduce 4M. i also check the
> /proc/buddyinfo, it seemes too.
> (i am looking inside kernel code, but not get clear at now).
>
> is remap_pfn_range should align to 2(n) * (page size) ?
This has nothing to do with remap_pfn_range but with the power of two
sized buckets used by the global free page pool. Any allocation with
get_free_pages will be rounded up to the next power of two. If that's a
real concern for you you could allocate a 4MB page then split the page
into a 2MB and two 1MB pages and free the 1MB page again.
Ralf
next prev parent reply other threads:[~2008-05-09 9:56 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-05-09 6:54 is remap_pfn_range should align to 2(n) * (page size) ? zhuzhenhua
2008-05-09 9:56 ` Ralf Baechle [this message]
2008-05-12 2:18 ` zhuzhenhua
2008-05-12 11:22 ` Ralf Baechle
2008-05-13 11:44 ` zhuzhenhua
2008-05-13 17:23 ` Ralf Baechle
2008-05-14 1:19 ` zhuzhenhua
2008-05-14 7:33 ` Geert Uytterhoeven
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