linux-kernel - Memory limits - mm_segment_t

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Date:	Wed, 29 Apr 2009 15:54:47 +0200
From:	Michal Simek <monstr@...str.eu>
To:	Arnd Bergmann <arnd@...db.de>,
	John Williams <john.williams@...alogix.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Memory limits - mm_segment_t - MAKE_MM_SEG

Hi all,

I look at some things which I need to clear for MMU Microblaze patches and
I would like to know your opinion about.

First of all I found that almost all archs use MAKE_MM_SEG macro which should be good
to move to generic location (asm-generic/uaccess.h ? )
#define MAKE_MM_SEG(s) ((mm_segment_t) { (s) })


The second thing is about place where is stored limit for processes -> mm_segment_t structure

Where is the proper location for storing mm_segment_t? Some arch use thread_info some of them
thread_struct

For microblaze case are used both -> that's definitely not correct.

Here is the small table for cpus which are in linux kernel and location and type for them.
The most of them uses thread_info structure for it and name is addr_limit.
The location of mm_segment_t is different too -> we should move it to any generic location too.
What do you think?

        location                     name           location      struct mm_segment_t
s390:   processor.h/thread_struct    mm_segment     processor.h   __u32 ar4
alpha:  thread_info.h/thread_info    addr_limit     processor.h  unsigned long seg
x86:    thread_info.h/thread_info    addr_limit     processor.h  unsigned long seg
ia64:   thread_info.h/thread_info    addr_limit     processor.h  unsigned long seg
mips:   thread_info.h/thread_info    addr_limit     processor.h  unsigned long seg
um:     thread_info.h/thread_info    addr_limit     uaccess.h    unsigned long seg
frv:    thread_info.h/thread_info    addr_limit     segment.h    unsigned long seg
cris:   thread_info.h/thread_info    addr_limit     segment.h    unsigned long seg
sh:     thread_info.h/thread_info    addr_limit     segment.h    unsigned long seg
h8300:  not_used     not_used                       segment.h    unsigned long seg
nm10300:thread_info.h/thread_info    addr_limit     processor.h  unsigned long seg
arm:    thread_info.h/thread_info    addr_limit     thread_info.h  typedef unsigned long mm_segment_t;
parisc: thread_info.h/thread_info    addr_limit     processor.h  int seq
m32r:   thread_info.h/thread_info    addr_limit     processor.h  unsigned long seg
xtensa: thread_info.h/thread_info    addr_limit     segment.h    unsigned long seg
avr32:  not_used     not_used                       uaccess.h    unsigned int is_user_space;
sparc:  processor_32.h/thread_struct  current_ds    processor_32.h  int seg
m68k:   not_used     not_used                       segment.h    unsigned long seg
blackfin:thread_info.h/thread_info    addr_limit    thread_info.h  typedef unsigned long mm_segment_t;
powerpc: processor.h/thread_struct  current_ds     processor.h  unsigned long seg


There is really mess in it and I would like to have good solution for Microblaze and I think
that will be good to have any generic solution and remove code duplication.

Thanks for your comments,
Michal


-- 
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
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