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Re: pgd_init() Patch

To: Geert Uytterhoeven <geert@linux-m68k.org>
Subject: Re: pgd_init() Patch
From: Jun Sun <jsun@mvista.com>
Date: Mon, 28 Jan 2002 12:04:58 -0800
Cc: Phil Thompson <phil@river-bank.demon.co.uk>, Linux/MIPS Development <linux-mips@oss.sgi.com>
References: <Pine.GSO.4.21.0201282052240.2836-100000@vervain.sonytel.be>
Sender: owner-linux-mips@oss.sgi.com
Geert Uytterhoeven wrote:
> 
> On Mon, 28 Jan 2002, Phil Thompson wrote:
> > - USER_PTRS_PER_PGD is defined as TASK_SIZE/PGDIR_SIZE. However,
> > because, TASK_SIZE is actually defined as one less that the maximum task
>            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > size there is a rounding error that means that USER_PTRS_PER_PGD works
>   ^^^^
> > out at 511 rather than 512. This means that entries 511 and 1023 of
> > swapper_pg_dir don't get initialised.
> >
> > The corresponding mips64 code has only the first call to pgd_init() and
> > each implementation of pgd_init() initialises PTRS_PER_PGD entries,
> > where PTRS_PER_PGD is simple defined as 1024.
> >
> > The attached patch applies the mips64 approach to the mips code.
> >
> > Should USER_PTRS_PER_PGD be defined as (TASK_SIZE/PGDIR_SIZE) + 1?
> 
> You mean ((TASK_SIZE)+1)/PGDIR_SIZE?
> 

No.  It should be

+#define USER_PTRS_PER_PGD      ((TASK_SIZE-1)/PGDIR_SIZE + 1)

Mathmatically, 

USER_PTRS_PER_PGD=ceil(TASK_SIZE/PGDIR_SIZE)

I submitted this patch to Ralf on Jan 03.  Ralf, any reason for not applying
this?  This formula ensures PTRS_PER_PGD is always correct irrespect of the
values of TAKS_SIZE and PGDIR_SIZE.

See this patch and other pending patches at

http://linux.junsun.net/patches/oss.sgi.com/submitted

Jun

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