Re: Re: config_discontigmem against add_memory_region

["Pichai Raghavan" <ragh_avan@rediffmail.com>]

HI,

Attached is the thread I had picked up and that I was talking 
about. Incidentally I too am using MIPS and have the same meory 
map as mentioned below.


----------- From here -----------------
On Tue, Oct 30, 2001 at 06:11:43PM +0800, Green wrote:
>I am porting Linux to R3912.
>
>There are two memory block on my target board.
>
>One is 16MB from 0x8000 0000 to 0x8100 0000.
>
>The other one is 16MB from 0x8200 0000 to 0x8300 0000.
>
>But I found kernel just managed the first memory block.
>
>How could I modify the kernel to support 32MB discontinuous 
>memory?
>
>Now I am trying to add entries to page table.
>It will halt at decompressing ramdisk.
>
>Has anyone resolve this kind of problem before?
The kernel support this type of memory architecture if you 
enable
CONFIG_DISCONTIGMEM. One machine which uses this feature is the 
Origin,
grep in arch/mips64 for CONFIG_DISCONTIGMEM. There are also 
several
ARM system using it.
As support for CONFIG_DISCONTIGMEM is less than perfect you should 
check
if your system allows for reconfiguration of memory as a single 
physically
contiguous chunk.
Don't use add_memory_region() in this case; that code only works 
well
for small holes in memory address space. Your holes are fairly 
large
so memory management would waste about 2mb if you would not use
CONFIG_DISCONTIGMEM.
   Ralf

------------- Till here -----------

Thanks
Raghav


On Thu, 09 May 2002 Patricia Gaughen wrote :
>
>   > Hi,
>   >
>   > If a Linux system has discontingous memory, then normal 
>practise
>   > is to call add_memory_region() before calling bootmem 
>allocator.
>
>I'm not sure why you are making this assumption.  What 
>architecture are you
>basing this on?  On i386, add_memory_region is called to fill in 
>the e820
>structure based on the info gotten from the e820 (this is all 
>done independent
>of discontigmem). This structure is then used to determine the 
>max_pfn,
>max_low_pfn and family.  This information is then used for 
>setuping up the
>bootmem allocator and then later the zones.
>
>   > In a thread on the net, there is a mention of using
>   > CONFIG_DISCONTIGMEM for huge memory hole(gain of 2MB for 
>16MB
>   > hole)
>
>Please send me a ptr to the thread you are referring to.
>
>   >
>   > How does one use CONFIG_DISCONTIGMEM? (is there any code
>   > available) And how does it manage to save space against
>   > add_memory_region?
>   >
>
>I have been working on CONFIG_DISCONTIGMEM support i386 and have 
>a patch
>that's available for download.  Feel free to check this out.  You 
>can get it
>off of sourceforge at
>
>http://sourceforge.net/project/showfiles.php?group_id=8875&release_id=87263
>
>Hope this helps,
>Pat
>
>--
>Patricia Gaughen (gone@us.ibm.com)
>IBM Linux Technology Center
>http://www.ibm.com/linux/ltc/
>
>

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