Go to file
Sumanth Korikkar c5f1e2d189 mm/memory_hotplug: introduce MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers
Patch series "implement "memmap on memory" feature on s390".

This series provides "memmap on memory" support on s390 platform.  "memmap
on memory" allows struct pages array to be allocated from the hotplugged
memory range instead of allocating it from main system memory.

s390 currently preallocates struct pages array for all potentially
possible memory, which ensures memory onlining always succeeds, but with
the cost of significant memory consumption from the available system
memory during boottime.  In certain extreme configuration, this could lead
to ipl failure.

"memmap on memory" ensures struct pages array are populated from self
contained hotplugged memory range instead of depleting the available
system memory and this could eliminate ipl failure on s390 platform.

On other platforms, system might go OOM when the physically hotplugged
memory depletes the available memory before it is onlined.  Hence, "memmap
on memory" feature was introduced as described in commit a08a2ae346
("mm,memory_hotplug: allocate memmap from the added memory range").

Unlike other architectures, s390 memory blocks are not physically
accessible until it is online.  To make it physically accessible two new
memory notifiers MEM_PREPARE_ONLINE / MEM_FINISH_OFFLINE are added and
this notifier lets the hypervisor inform that the memory should be made
physically accessible.  This allows for "memmap on memory" initialization
during memory hotplug onlining phase, which is performed before calling
MEM_GOING_ONLINE notifier.

Patch 1 introduces MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE memory notifiers
to prepare the transition of memory to and from a physically accessible
state.  New mhp_flag MHP_OFFLINE_INACCESSIBLE is introduced to ensure
altmap cannot be written when adding memory - before it is set online. 
This enhancement is crucial for implementing the "memmap on memory"
feature for s390 in a subsequent patch.

Patches 2 allocates vmemmap pages from self-contained memory range for
s390.  It allocates memory map (struct pages array) from the hotplugged
memory range, rather than using system memory by passing altmap to vmemmap
functions.

Patch 3 removes unhandled memory notifier types on s390.

Patch 4 implements MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE memory notifiers
on s390.  MEM_PREPARE_ONLINE memory notifier makes memory block physical
accessible via sclp assign command.  The notifier ensures self-contained
memory maps are accessible and hence enabling the "memmap on memory" on
s390.  MEM_FINISH_OFFLINE memory notifier shifts the memory block to an
inaccessible state via sclp unassign command.

Patch 5 finally enables MHP_MEMMAP_ON_MEMORY on s390.


This patch (of 5):

Introduce MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE memory notifiers to
prepare the transition of memory to and from a physically accessible
state.  This enhancement is crucial for implementing the "memmap on
memory" feature for s390 in a subsequent patch.

Platforms such as x86 can support physical memory hotplug via ACPI.  When
there is physical memory hotplug, ACPI event leads to the memory addition
with the following callchain:

acpi_memory_device_add()
  -> acpi_memory_enable_device()
     -> __add_memory()

After this, the hotplugged memory is physically accessible, and altmap
support prepared, before the "memmap on memory" initialization in
memory_block_online() is called.

On s390, memory hotplug works in a different way.  The available hotplug
memory has to be defined upfront in the hypervisor, but it is made
physically accessible only when the user sets it online via sysfs,
currently in the MEM_GOING_ONLINE notifier.  This is too late and "memmap
on memory" initialization is performed before calling MEM_GOING_ONLINE
notifier.

During the memory hotplug addition phase, altmap support is prepared and
during the memory onlining phase s390 requires memory to be physically
accessible and then subsequently initiate the "memmap on memory"
initialization process.

The memory provider will handle new MEM_PREPARE_ONLINE /
MEM_FINISH_OFFLINE notifications and make the memory accessible.

The mhp_flag MHP_OFFLINE_INACCESSIBLE is introduced and is relevant when
used along with MHP_MEMMAP_ON_MEMORY, because the altmap cannot be written
(e.g., poisoned) when adding memory -- before it is set online.  This
allows for adding memory with an altmap that is not currently made
available by a hypervisor.  When onlining that memory, the hypervisor can
be instructed to make that memory accessible via the new notifiers and the
onlining phase will not require any memory allocations, which is helpful
in low-memory situations.

All architectures ignore unknown memory notifiers.  Therefore, the
introduction of these new notifiers does not result in any functional
modifications across architectures.

Link: https://lkml.kernel.org/r/20240108132747.3238763-1-sumanthk@linux.ibm.com
Link: https://lkml.kernel.org/r/20240108132747.3238763-2-sumanthk@linux.ibm.com
Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Suggested-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-02-21 16:00:01 -08:00
Documentation Kbuild fixes for v6.8 (2nd) 2024-02-18 10:09:25 -08:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
arch Kbuild fixes for v6.8 (2nd) 2024-02-18 10:09:25 -08:00
block blk-iocost: Fix an UBSAN shift-out-of-bounds warning 2024-02-08 10:11:39 -07:00
certs This update includes the following changes: 2023-11-02 16:15:30 -10:00
crypto crypto: algif_hash - Remove bogus SGL free on zero-length error path 2024-02-02 18:08:12 +08:00
drivers mm/memory_hotplug: introduce MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers 2024-02-21 16:00:01 -08:00
fs bcachefs fixes for v6.8-rc5 2024-02-17 13:17:32 -08:00
include mm/memory_hotplug: introduce MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers 2024-02-21 16:00:01 -08:00
init update workarounds for gcc "asm goto" issue 2024-02-15 11:14:33 -08:00
io_uring io_uring/net: fix multishot accept overflow handling 2024-02-14 18:30:19 -07:00
ipc shm: Slim down dependencies 2023-12-20 19:26:31 -05:00
kernel Probes fixes for v6.8-rc4: 2024-02-17 07:59:47 -08:00
lib maple_tree: fix comment describing mas_node_count_gfp() 2024-02-21 16:00:01 -08:00
mm mm/memory_hotplug: introduce MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers 2024-02-21 16:00:01 -08:00
net Including fixes from can, wireless and netfilter. 2024-02-15 11:39:27 -08:00
rust Rust changes for v6.8 2024-01-11 13:05:41 -08:00
samples work around gcc bugs with 'asm goto' with outputs 2024-02-09 15:57:48 -08:00
scripts kallsyms: ignore ARMv4 thunks along with others 2024-02-15 22:44:56 +09:00
security lsm/stable-6.8 PR 20240215 2024-02-16 07:58:43 -08:00
sound ALSA: usb-audio: More relaxed check of MIDI jack names 2024-02-15 16:56:05 +01:00
tools selftests/mm: uffd-unit-test check if huge page size is 0 2024-02-20 14:20:48 -08:00
usr Kbuild updates for v6.8 2024-01-18 17:57:07 -08:00
virt Generic: 2024-01-17 13:03:37 -08:00
.clang-format clang-format: Update with v6.7-rc4's `for_each` macro list 2023-12-08 23:54:38 +01:00
.cocciconfig
.editorconfig Add .editorconfig file for basic formatting 2023-12-28 16:22:47 +09:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Add .editorconfig file for basic formatting 2023-12-28 16:22:47 +09:00
.mailmap MAINTAINERS: mailmap: update Shakeel's email address 2024-02-20 14:20:50 -08:00
.rustfmt.toml rust: add `.rustfmt.toml` 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: supplement of zswap maintainers update 2024-01-25 23:52:21 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: mailmap: update Shakeel's email address 2024-02-20 14:20:50 -08:00
Makefile Linux 6.8-rc5 2024-02-18 12:56:25 -08:00
README

README

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 Restructured Text 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.