Re: [Qemu-devel] [PATCH 0/6] pc: bring ACPI table size below to 2.0 levels, try fixing -initrd for good

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> However, there is another problem.  As the ACPI tables grow, we need
> to move the address at which linuxboot.bin loads the initrd.  This
> address is placed close to the end of memory, but it is QEMU that
> tells linuxboot.bin where exactly the initrd is to be loaded.  And
> QEMU cannot really know how much high memory SeaBIOS will use, because
> QEMU does not know the final e820 memory map.
> 
> The solution would be to let linuxboot.bin parse the memory map and
> ignore the suggested initrd base address, but that's tedious.  In the
> meanwhile, we can just assume that most of the need comes from the ACPI
> tables (which is in fact true: patch 3 adds a fixed 32k extra just in
> case) and dynamically resize the padding.

Hmm.  That assumes we are running seabios, where we know how much memory
we actually need.

IMHO we should either really parse the memory map, or reserve more
space.

IIRC it doesn't matter that much where we load the initrd.  It should
not be just after the kernel, because the kernel needs some space to
unpack itself and for early allocations such as initial page tables.
This is where the common practice to load the initrd high comes from.
But whenever we leave 128k or 16m between initrd and top-of-memory
doesn't make much of a difference.

cheers,
  Gerd