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On s390, memory blocks are not currently removed via
arch_remove_memory(). With upcoming dynamic memory (de)configuration
support, runtime removal of memory blocks is possible. This internally
involves tearing down identity mapping, virtual memory mappings and
freeing the physical memory backing the struct pages metadata.
During early boot, physical memory used to back the struct pages
metadata in vmemmap is allocated through:
setup_arch()
-> sparse_init()
-> sparse_init_nid()
-> __populate_section_memmap()
-> vmemmap_alloc_block_buf()
-> sparse_buffer_alloc()
-> memblock_alloc()
Here, sparse_init_nid() sets up virtual-to-physical mapping for struct
pages backed by memblock_alloc(). This differs from runtime addition of
hotplug memory which uses the buddy allocator later.
To correctly free identity mappings, vmemmap mappings during hot-remove,
boot-time and runtime allocations must be distinguished using the
PageReserved bit:
* Boot-time memory, such as identity-mapped page tables allocated via
boot_crst_alloc() and reserved via reserve_pgtables() is marked
PageReserved in memmap_init_reserved_pages().
* Physical memory backing vmemmap (struct pages from memblock_alloc())
is also marked PageReserved similarly.
During teardown, PageReserved bit is checked to distinguish between
boot-time allocation or buddy allocation.
This is similar to commit 645d5ce2f7 ("powerpc/mm/radix: Fix PTE/PMD
fragment count for early page table mappings")
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.