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Sumanth Korikkar says: ==================== Provide a new interface for dynamic configuration and deconfiguration of hotplug memory on s390, allowing with/without memmap_on_memory support. It is a follow up on the discussion with David when introducing memmap_on_memory support for s390 and support dynamic (de)configuration of memory: https://lore.kernel.org/all/ee492da8-74b4-4a97-8b24-73e07257f01d@redhat.com/ https://lore.kernel.org/all/20241202082732.3959803-1-sumanthk@linux.ibm.com/ The original motivation for introducing memmap_on_memory on s390 was to avoid using online memory to store struct pages metadata, particularly for standby memory blocks. This became critical in cases where there was an imbalance between standby and online memory, potentially leading to boot failures due to insufficient memory for metadata allocation. To address this, memmap_on_memory was utilized on s390. However, in its current form, it adds struct pages metadata at the start of each memory block at the time of addition (only standby memory), and this configuration is static. It cannot be changed at runtime (When the user needs continuous physical memory). Inorder to provide more flexibility to the user and overcome the above limitation, add an option to dynamically configure and deconfigure hotpluggable memory block with/without memmap_on_memory. With the new interface, s390 will not add all possible hotplug memory in advance, like before, to make it visible in sysfs for online/offline actions. Instead, before memory block can be set online, it has to be configured via a new interface in /sys/firmware/memory/memoryX/config, which makes s390 similar to others. i.e. Adding of hotpluggable memory is controlled by the user instead of adding it at boottime. s390 kernel sysfs interface to configure/deconfigure memory with memmap_on_memory (with upcoming lsmem changes): * Initial memory layout: lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY RANGE SIZE STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY 0x00000000-0x7fffffff 2G online 0-15 yes no 0x80000000-0xffffffff 2G offline 16-31 no yes * Configure memory echo 1 > /sys/firmware/memory/memory16/config lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY RANGE SIZE STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY 0x00000000-0x7fffffff 2G online 0-15 yes no 0x80000000-0x87ffffff 128M offline 16 yes yes 0x88000000-0xffffffff 1.9G offline 17-31 no yes * Deconfigure memory echo 0 > /sys/firmware/memory/memory16/config lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY RANGE SIZE STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY 0x00000000-0x7fffffff 2G online 0-15 yes no 0x80000000-0xffffffff 2G offline 16-31 no yes * Enable memmap_on_memory and online it. (Deconfigure first) echo 0 > /sys/devices/system/memory/memory5/online echo 0 > /sys/firmware/memory/memory5/config lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY RANGE SIZE STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY 0x00000000-0x27ffffff 640M online 0-4 yes no 0x28000000-0x2fffffff 128M offline 5 no no 0x30000000-0x7fffffff 1.3G online 6-15 yes no 0x80000000-0xffffffff 2G offline 16-31 no yes (Enable memmap_on_memory and online it) echo 1 > /sys/firmware/memory/memory5/memmap_on_memory echo 1 > /sys/firmware/memory/memory5/config echo 1 > /sys/devices/system/memory/memory5/online lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY RANGE SIZE STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY 0x00000000-0x27ffffff 640M online 0-4 yes no 0x28000000-0x2fffffff 128M online 5 yes yes 0x30000000-0x7fffffff 1.3G online 6-15 yes no 0x80000000-0xffffffff 2G offline 16-31 no yes * Disable memmap_on_memory and online it. (Deconfigure first) echo 0 > /sys/devices/system/memory/memory5/online echo 0 > /sys/firmware/memory/memory5/config lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY RANGE SIZE STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY 0x00000000-0x27ffffff 640M online 0-4 yes no 0x28000000-0x2fffffff 128M offline 5 no yes 0x30000000-0x7fffffff 1.3G online 6-15 yes no 0x80000000-0xffffffff 2G offline 16-31 no yes (Disable memmap_on_memory and online it) echo 0 > /sys/firmware/memory/memory5/memmap_on_memory echo 1 > /sys/firmware/memory/memory5/config echo 1 > /sys/devices/system/memory/memory5/online lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY RANGE SIZE STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY 0x00000000-0x7fffffff 2G online 0-15 yes no 0x80000000-0xffffffff 2G offline 16-31 no yes * Userspace changes: lsmem/chmem tool is also changed to use the new interface. I will send it to util-linux soon. Patch 1 adds support for removal of boot-allocated memory blocks. Patch 2 provides option to dynamically configure and deconfigure memory with/without memmap_on_memory. Patch 3 removes MHP_OFFLINE_INACCESSIBLE from s390. The mhp flag was used to mark memory as not accessible until memory hotplug online phase begins. However, with patch 2, it is no longer essential. Memory can be brought to accessible state before adding memory, as the memory is added during runttime now instead of boottime. Patch 4 removes the MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers. It is no longer needed. Memory can be brought to accessible state before adding memory now, with runtime (de)configuration of memory. Note: The patches apply to the linux-next branch. v3: Thanks David * Avoid goto label in create_standby_sclp_mems(). * Use unsigned long instead of u64. * Add Acked-by. v2: Thanks David * Rename struct mblock/mblock_arg with struct sclp_mem/sclp_mem_arg. * Rename all mblocks/mblock references with sclp_mems/sclp_mem - structures, functions. * Rename create_online_mblock() with create_configured_sclp_mem(). * Rename config_mblock_show()/config_mblock_store() with config_sclp_mem_show()/config_sclp_mem_store(). * Remove contains_standby_increment() and sclp_mem_notifier. sclp mem state change is performed when adding/removing memory. sclp memory notifier - no longer needed with this patchset. * Recover sclp mem state when add_memory() fails. * Refactor and add function init_sclp_mem(). * Use unsigned long instead of unsigned long long. * Simplify and correct kobj handling. Thanks Heiko. ==================== 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.