linux-kernel - Re: [GIT PULL] x86, percpu: implement and use reserved percpu alloc

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Date:	Fri, 6 Mar 2009 09:06:35 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Tejun Heo <tj@...nel.org>
Cc:	rusty@...tcorp.com.au, tglx@...utronix.de, x86@...nel.org,
	linux-kernel@...r.kernel.org, hpa@...or.com, efault@....de,
	jaswinder@...nel.org, cooloney@...nel.org
Subject: Re: [GIT PULL] x86, percpu: implement and use reserved percpu alloc


* Tejun Heo <tj@...nel.org> wrote:

> Hello,
> 
> Please pull from the following git vector.
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git tj-percpu
> 
> This patchset implements reserved percpu alloc from the first 
> chunk and uses it for static perpcu variables in modules on 
> x86_64.  This is necessary because x86_64 expects symbols to 
> be relocatable using 32bit relocations but dynamic percpu 
> allocation does not guarantee it leading to relocation 
> overflow during module load.
> 
> This can happen to any of the x86_64 percpu first chunk 
> allocators but the embedding allocator is most likely to 
> trigger it as the first chunk is located in the normal kernel 
> memory allocation area while all the other chunks will be 
> allocated in the vmalloc area which is very far from the first 
> chunk.
> 
> This type of reservation will be necessary for other 
> architectures too where addressing mode used for percpu acess 
> uses offsets with limited range to access symbols (e.g. ia64 
> w/ the magic 64k percpu page).
> 
> This problem was first reported and bisected by Mike 
> Galbraith[2].
> 
> This patchset is against the current x86/core/percpu[1] and contains
> the following patches.
> 
>  0001-percpu-clean-up-percpu-constants.patch
>  0002-percpu-cosmetic-renames-in-pcpu_setup_first_chunk.patch
>  0003-percpu-improve-first-chunk-initial-area-map-handlin.patch
>  0004-percpu-use-negative-for-auto-for-pcpu_setup_first_c.patch
>  0005-x86-make-embedding-percpu-allocator-return-excessiv.patch
>  0006-percpu-add-an-indirection-ptr-for-chunk-page-map-ac.patch
>  0007-percpu-module-implement-reserved-allocation-and-us.patch
>  0008-x86-percpu-setup-reserved-percpu-area-for-x86_64.patch
> 
> 0001-0004 makes misc updates to percpu in preparation of later 
> changes.  0005 fixes a case where excessive memory can be set 
> aside in the first chunk when using the embedding allocator.  
> 0006-0008 implement reserved allocation and use it for x86_64.
> 
> Bryan Wu, can you please review #0001?  It contains small 
> change in blackfin.  It's mostly trivial but just in case.
> 
> Diffstat follows.
> 
>  arch/blackfin/include/asm/percpu.h |   10 -
>  arch/x86/kernel/setup_percpu.c     |   73 +++++++---
>  include/linux/percpu.h             |   60 +++-----
>  kernel/module.c                    |    2 
>  mm/percpu.c                        |  267 ++++++++++++++++++++++++++-----------
>  5 files changed, 274 insertions(+), 138 deletions(-)

Pulled, thanks Tejun!

	Ingo
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