PATCH: increase heap size for (gpt)zfsboot

[John Baldwin]

On Monday 07 December 2009 7:01:03 pm Matt Reimer wrote:
> Enlarge the heap size for gptzfsboot and zfsboot. This is necessary so
> the ZFS code has enough memory to handle decompression and error
> recovery.
> 
> Before this patch the heap grew from the end of the (gpt)zfsboot code
> and static data up to 640KB, possibly overrunning the stack. Now the
> heap is located at 16MB-64MB.
> 
> Note that this requires machines with at least 64MB RAM, but this is
> not likely to be a problem on any machine running ZFS.
> 
> Sponsored by: VPOP Technologies, Inc.
> 
> Matt Reimer

Unfortunately the 16M - 64M range may not all be useable RAM.  It may contain 
ACPI tables, etc.  A robust approach would involve walking the SMAP, etc.  I 
just committed some changes to sys/boot/i386/loader/biosmem.c that make it 
smarter about choosing a heap region.  I suggest adopting that algorithm for 
figuring out a safe heap range.  zfsboot and gptzfsboot should have enough 
free space to take the bios_getmem() function.  You can increase the minimum 
heap size beyond 3M if desired (though 3M is the minimum the loader will 
guarantee currently, and if ZFS needs more than that it likely needs to be 
changed in both places).

-- 
John Baldwin