Re: [PATCH V3 2/2] mm/memblock: Add support for excluded memoryareas

[Philipp Hachtmann]

Hello Grygorii,

thank you for your comments.

To clarify we have the following requirements for memblock:

(1) Reserved areas can be declared before memory is added.
(2) The physical memory is detected once only.
(3) The free memory (i.e. not reserved) memory can be iterated to add
it to the buddy allocator.
(4) Memory designated to be mapped into the kernel address space can be
iterated.
(5) Kdump on s390 requires knowledge about the full system memory
layout.

The s390 kdump implementation works a bit different from the
implementation on other architectures: The layout is not taken from the
production system and saved for the kdump kernel. Instead the kdump
kernel needs to gather information about the whole memory without
respect to locked out areas (like mem= and OLDMEM etc.).

Without kdump's requirement it would of course be suitable and easy
just to remove memory from memblock.memory. But then this information
is lost for later use by kdump.

The patch does not change any behaviour of the current API - whether it
is enabled or not.

The current patch seems to be overly complicated.
The following patch contains only the nomap functionality without any
cleanup and refactoring. I will post a V4 patch set which will contain
this patch.

Kind regards

Philipp