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Provide a new interface for dynamic configuration and deconfiguration of hotplug memory, 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 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 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. The s390 kernel sysfs interface to configure and deconfigure memory is as follows (considering the 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 sys="/sys" 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 3. Enable memmap_on_memory and online it. 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 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 4. Disable memmap_on_memory and online it. 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 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 Acked-by: Heiko Carstens <hca@linux.ibm.com> Acked-by: David Hildenbrand <david@redhat.com> Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com> Signed-off-by: Heiko Carstens <hca@linux.ibm.com> |
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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.