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From: Dave Hansen <dave@linux.vnet.ibm.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: KyongHo Cho <pullip.cho@samsung.com>,
	Kukjin Kim <kgene.kim@samsung.com>,
	KeyYoung Park <keyyoung.park@samsung.com>,
	linux-kernel@vger.kernel.org, Ilho Lee <ilho215.lee@samsung.com>,
	linux-mm@kvack.org, linux-samsung-soc@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] ARM: mm: Regarding section when dealing with meminfo
Date: Mon, 24 Jan 2011 08:52:17 -0800	[thread overview]
Message-ID: <1295887937.11047.119.camel@nimitz> (raw)
In-Reply-To: <20110123180532.GA3509@n2100.arm.linux.org.uk>

On Sun, 2011-01-23 at 18:05 +0000, Russell King - ARM Linux wrote:
> On Thu, Jan 20, 2011 at 10:11:27AM -0800, Dave Hansen wrote:
> > On Thu, 2011-01-20 at 18:01 +0000, Russell King - ARM Linux wrote:
> > > > The x86 version of show_mem() actually manages to do this without any
> > > > #ifdefs, and works for a ton of configuration options.  It uses
> > > > pfn_valid() to tell whether it can touch a given pfn.
> > > 
> > > x86 memory layout tends to be very simple as it expects memory to
> > > start at the beginning of every region described by a pgdat and extend
> > > in one contiguous block.  I wish ARM was that simple.
> > 
> > x86 memory layouts can be pretty funky and have been that way for a long
> > time.  That's why we *have* to handle holes in x86's show_mem().  My
> > laptop even has a ~1GB hole in its ZONE_DMA32:
> 
> If x86 is soo funky, I suggest you try the x86 version of show_mem()
> on an ARM platform with memory holes.  Make sure you try it with
> sparsemem as well...

x86 uses the generic lib/ show_mem().  It works for any holes, as long
as they're expressed in one of the memory models so that pfn_valid()
notices them.

ARM looks like its pfn_valid() is backed up by searching the (ASM
arch-specific) memblocks.  That looks like it would be fairly slow
compared to the other pfn_valid() implementations and I can see why it's
being avoided in show_mem().

Maybe we should add either the MAX_ORDER or section_nr() trick to the
lib/ implementation.  I bet that would use pfn_valid() rarely enough to
meet any performance concerns.

-- Dave


  reply	other threads:[~2011-01-24 16:54 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-20  9:45 KyongHo Cho
2011-01-20 14:28 ` Minchan Kim
2011-01-20 17:25   ` Dave Hansen
     [not found]   ` <AANLkTinXAiShaf1f69ufVHg7KPaY5j=jmOTtK71GNNp5@mail.gmail.com>
2011-01-20 17:43     ` Minchan Kim
2011-01-20 17:44       ` Minchan Kim
2011-01-20 17:52         ` KyongHo Cho
2011-01-20 17:20 ` Dave Hansen
     [not found]   ` <AANLkTi=nsAOtLPK75Wy5Rm8pfWob8xTP5259DyYuxR9J@mail.gmail.com>
2011-01-20 17:48     ` KyongHo Cho
2011-01-20 18:04     ` Dave Hansen
2011-01-20 18:01   ` Russell King - ARM Linux
2011-01-20 18:11     ` Dave Hansen
2011-01-23 18:05       ` Russell King - ARM Linux
2011-01-24 16:52         ` Dave Hansen [this message]
2011-01-24 17:58           ` Russell King - ARM Linux
2011-01-24 18:47             ` Dave Hansen
2011-01-25  0:33             ` KyongHo Cho
2011-01-21  2:12     ` KyongHo Cho
2011-01-21 10:38       ` Russell King - ARM Linux
2011-01-21 11:15         ` KyongHo Cho

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