linux-kernel - Re: [RFC PATCH 0/6] ARM: use NO_BOOTMEM on default configuration

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Message-ID: <20130422082225.GB19454@lge.com>
Date:	Mon, 22 Apr 2013 17:22:25 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Russell King <linux@....linux.org.uk>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Nicolas Pitre <nico@...aro.org>,
	Will Deacon <will.deacon@....com>
Subject: Re: [RFC PATCH 0/6] ARM: use NO_BOOTMEM on default configuration

On Mon, Mar 25, 2013 at 01:11:08PM +0900, Joonsoo Kim wrote:
> Currently, ARM use traditional 'bootmem' allocator. It use a bitmap for
> managing memory space, so initialize a bitmap at first step. It is
> a needless overhead if we use 'nobootmem'. 'nobootmem' use a memblock
> allocator internally, so there is no additional initializing overhead.
> In addition, if we use 'nobootmem', we can save small amount of memory,
> because 'nobootmem' manage memory space as byte unit. However, 
> 'bootmem' manage it as page unit, so some space is wasted,
> although it is very small. On my system, 20 KB memories can be saved. :)
> Using 'nobootmem' have another advantage. Before initializing 'bootmem'
> allocator, we use memblock allocator. If we use memblock allocator
> after initializing 'bootmem' by mistake, there is possible problem.
> Patch '1/6' is good example of this case. 'nobootmem' use memblock
> allocator internally, so these risk will be disappeared.
> 
> There is one stopper to enable NO_BOOTMEM, it is max_low_pfn.
> nobootmem use max_low_pfn for computing boundary in free_all_bootmem()
> So we need proper value to max_low_pfn.
> But, there is some difficulty related to max_low_pfn. max_low_pfn is used
> for two meanings in various architectures. One is for number of pages
> in lowmem and the other is for maximum lowmem pfn. Now, in ARM, it is used
> as number of pages in lowmem. You can get more information in below link.
> http://lwn.net/Articles/543408/
> http://lwn.net/Articles/543424/
>     
> As I investigated, architectures which use max_low_pfn as maximum pfn are
> more than others, so IMHO, to change meaning of max_low_pfn to maximum pfn
> is preferable solution to me. This patchset change max_low_pfn as maximum
> lowmem pfn in ARM. In addition, min_low_pfn, max_pfn is assigned according
> to this criteria.
> 
> AFAIK, there is no real user for max_low_pfn except block/blk-setting.c
> and blk-setting.c assume that max_low_pfn is maximum lowmem pfn,
> so this patch may not harm anything. But, I'm not expert about this,
> so please let me know what I am missing.
> 
> I did some working test on my android device and it worked. :)
> Feel free to give me some opinion about this patset.
> This patchset is based on v3.9-rc4.
> 
> Thanks.
> 
> Joonsoo Kim (6):
>   ARM, TCM: initialize TCM in paging_init(), instead of setup_arch()
>   ARM, crashkernel: use ___alloc_bootmem_node_nopanic() for reserving
>     memory
>   ARM, crashkernel: correct total_mem size in reserve_crashkernel()
>   ARM, mm: don't do arm_bootmem_init() if CONFIG_NO_BOOTMEM
>   ARM, mm: change meaning of max_low_pfn to maximum pfn for nobootmem
>   ARM, mm: enable NO_BOOTMEM for default ARM build
> 
>  arch/arm/Kconfig        |    1 +
>  arch/arm/kernel/setup.c |   22 ++++++++--------------
>  arch/arm/kernel/tcm.c   |    1 -
>  arch/arm/kernel/tcm.h   |   17 -----------------
>  arch/arm/mm/init.c      |   19 ++++++++++++-------
>  arch/arm/mm/mmu.c       |    2 ++
>  arch/arm/mm/tcm.h       |   17 +++++++++++++++++
>  7 files changed, 40 insertions(+), 39 deletions(-)
>  delete mode 100644 arch/arm/kernel/tcm.h
>  create mode 100644 arch/arm/mm/tcm.h

Hello, guys.

Could you review and comment this patchset?
[1/6] is already merged, but others wait for someone's review :)

Thanks.

> 
> -- 
> 1.7.9.5
> 
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