[gPXE-devel] Expand heap size

[Michael Brown]

On Friday 04 Jun 2010 14:30:52 Guo-Fu Tseng wrote:
> I've come up with an idea about expanding heap memory,
> by relocating the heap to the end of gPXE's used memory.
> 
> More detail can see my note:
> http://etherboot.org/wiki/soc/2010/cooldavid/notes/expandheap
> 
> And here is the commit diff:
> http://bbs.cooldavid.org/git/?p=gpxe.git;a=commitdiff;h=bd912047fffeebe409a
> 785f88df58803cfde17cb
> 
> I've tested it, and it works fine with i386 arch with librm.
> But I'm not sure if it is reasonable, and I might miss concern
> something.
> 
> Asking for opinions. :)

Three things:

1. Any memory (including heap memory) used is potentially going to be 
permanently lost for the duration of the system boot.  (SAN boot mechanisms do 
not get a chance to unhide memory.)

2. If you want a larger heap, can you not just increase HEAP_SIZE?  I don't 
see why the rest of the patch is necessary.

3. By increasing the total memory footprint beyond 1MB, you lose the guarantee 
of residing entirely within a region with A20=0.  iPXE will work in a region 
with A20=1, but gPXE may fail.

Michael