linux-kernel - Re: Memory limits - mm_segment_t

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Date:	Wed, 29 Apr 2009 16:03:16 +0200
From:	Michal Simek <michal.simek@...alogix.com>
To:	monstr@...str.eu
CC:	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: Re: Memory limits - mm_segment_t - MAKE_MM_SEG

Michal Simek wrote:
> 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
>
>   
+ move some macros to generic location too.
#define get_ds()      (KERNEL_DS)

+ get_fs(), set_fs(), segment_eq() after sync changes above

Michal





-- 
Michal Simek, Ing. (M.Eng)
PetaLogix - Linux Solutions for a Reconfigurable World
w: www.petalogix.com p: +61-7-30090663,+42-0-721842854 f: +61-7-30090663

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