This patch-set aims to solve some problems at system boot time to enhance memory hotplug functionality.
[Background] The Linux kernel cannot migrate pages used by the kernel because of the kernel direct mapping. Since va = pa + PAGE_OFFSET, if the physical address is changed, we cannot simply update the kernel pagetable. On the contrary, we have to update all the pointers pointing to the virtual address, which is very difficult to do. In order to do memory hotplug, we should prevent the kernel to use hotpluggable memory. In ACPI, there is a table named SRAT(System Resource Affinity Table). It contains system NUMA info (CPUs, memory ranges, PXM), and also a flag field indicating which memory ranges are hotpluggable. [Problem to be solved] At the very early time when the system is booting, we use a bootmem allocator, named memblock, to allocate memory for the kernel. memblock will start to work before the kernel parse SRAT, which means memblock won't know which memory is hotpluggable before SRAT is parsed. So at this time, memblock could allocate hotpluggable memory for the kernel to use permanently. For example, the kernel may allocate pagetables in hotpluggable memory, which cannot be freed when the system is up. So we have to prevent memblock allocating hotpluggable memory for the kernel at the early boot time. [Earlier solutions] We have tried to parse SRAT earlier, before memblock is ready. To do this, we also have to do ACPI_INITRD_TABLE_OVERRIDE earlier. Otherwise the override tables won't be able to effect. This is not that easy to do because memblock is ready before direct mapping is setup. So Yinghai split the ACPI_INITRD_TABLE_OVERRIDE procedure into two steps: find and copy. Please refer to the following patch-set: https://lkml.org/lkml/2013/6/13/587 To this solution, tj gave a lot of comments and the following suggestions. [Suggestion from tj] tj mainly gave the following suggestions: 1. Necessary reordering is OK, but we should not rely on reordering to achieve the goal because it makes the kernel too fragile. 2. Memory allocated to kernel for temporary usage is OK because it will be freed when the system is up. Doing relocation for permanent allocated hotpluggable memory will make the the kernel more robust. 3. Need to enhance memblock to discover and complain if any hotpluggable memory is allocated to kernel. After a long thinking, we choose not to do the relocation for the following reasons: 1. It's easy to find out the allocated hotpluggable memory. But memblock will merge the adjoined ranges owned by different users and used for different purposes. It's hard to find the owners. 2. Different memory has different way to be relocated. I think one function for each kind of memory will make the code too messy. 3. Pagetable could be in hotpluggable memory. Relocating pagetable is too difficult and risky. We have to update all PUD, PMD pages. And also, ACPI_INITRD_TABLE_OVERRIDE and parsing SRAT procedures are not long after pagetable is initialized. If we relocate the pagetable not long after it was initialized, the code will be very ugly. [Solution in this patch-set] In this patch-set, we still do the reordering, but in a new way. 1. Improve memblock with flags, so that it is able to differentiate memory regions for different usage. And also a MEMBLOCK_HOTPLUG flag to mark hotpluggable memory. 2. When memblock is ready (memblock_x86_fill() is called), initialize acpi_gbl_root_table_list, fulfill all the ACPI tables' phys addrs. Now, we have all the ACPI tables' phys addrs provided by firmware. 3. Check if there is a SRAT in initrd file used to override the one provided by firmware. If so, get its phys addr. 4. If no override SRAT in initrd, get the phys addr of the SRAT provided by firmware. Now, we have the phys addr of the to be used SRAT, the one in initrd or the one in firmware. 5. Parse only the memory affinities in SRAT, find out all the hotpluggable memory regions and mark them in memblock.memory with MEMBLOCK_HOTPLUG flag. 6. The kernel goes through the current path. Any other related parts, such as ACPI_INITRD_TABLE_OVERRIDE path, the current parsing ACPI tables pathes, global variable numa_meminfo, and so on, are not modified. They work as before. 7. Make memblock default allocator skip hotpluggable memory. 8. Introduce movablenode boot option to allow users to enable and disable this functionality. In summary, in order to get hotpluggable memory info as early as possible, this patch-set only parse memory affinities in SRAT one more time right after memblock is ready, and leave all the other pathes untouched. With the hotpluggable memory info, we can arrange hotpluggable memory in ZONE_MOVABLE to prevent the kernel to use it. change log v2 RESEND -> v3: 1. As Rafael and Lv Zheng suggested, split acpi global root table list initialization procedure into two steps: install and override. And do the "install" step earlier. 2. Fix some little problems found by Toshi. change log v2 -> v2 RESEND: According to Toshi's advice: 1. Rename acpi_invalid_table() to acpi_verify_table(). 2. Rename acpi_root_table_init() to early_acpi_boot_table_init(). 3. Rename INVALID_TABLE() to ACPI_INVALID_TABLE(). 4. Check if ramdisk is present in early_acpi_override_srat(). 5. Check if ACPI is disabled in acpi_boot_table_init(). 6. Rebased to Linux 3.11-rc3. change log v1 -> v2: 1. According to Tejun's advice, make ACPI side report which memory regions are hotpluggable, and memblock side handle the memory allocation. 2. Change "movablecore=acpi" boot option to "movablenode" boot option. Thanks. Tang Chen (24): acpi: Print Hot-Pluggable Field in SRAT. earlycpio.c: Fix the confusing comment of find_cpio_data(). acpi: Remove "continue" in macro INVALID_TABLE(). acpi: Introduce acpi_verify_initrd() to check if a table is invalid. acpi, acpica: Split acpi_tb_install_table() into two parts. acpi, acpica: Call two new functions instead of acpi_tb_install_table() in acpi_tb_parse_root_table(). acpi, acpica: Split acpi_tb_parse_root_table() into two parts. acpi, acpica: Call two new functions instead of acpi_tb_parse_root_table() in acpi_initialize_tables(). acpi, acpica: Split acpi_initialize_tables() into two parts. x86, acpi: Call two new functions instead of acpi_initialize_tables() in acpi_table_init(). x86, acpi: Split acpi_table_init() into two parts. x86, acpi: Rename check_multiple_madt() and make it global. x86, acpi: Split acpi_boot_table_init() into two parts. x86, acpi: Initialize acpi golbal root table list earlier. x86: Make get_ramdisk_{image|size}() global. x86, acpica, acpi: Try to find if SRAT is overrided earlier. x86, acpica, acpi: Try to find SRAT in firmware earlier. x86, acpi, numa, mem_hotplug: Find hotpluggable memory in SRAT memory affinities. x86, numa, mem_hotplug: Skip all the regions the kernel resides in. memblock, numa: Introduce flag into memblock. memblock, mem_hotplug: Introduce MEMBLOCK_HOTPLUG flag to mark hotpluggable regions. memblock, mem_hotplug: Make memblock skip hotpluggable regions by default. mem-hotplug: Introduce movablenode boot option to {en|dis}able using SRAT. x86, numa, acpi, memory-hotplug: Make movablenode have higher priority. Yasuaki Ishimatsu (1): x86: get pg_data_t's memory from other node Documentation/kernel-parameters.txt | 15 ++ arch/x86/include/asm/setup.h | 21 +++ arch/x86/kernel/acpi/boot.c | 32 +++-- arch/x86/kernel/setup.c | 42 +++--- arch/x86/mm/numa.c | 5 +- arch/x86/mm/srat.c | 11 +- drivers/acpi/acpica/actables.h | 2 + drivers/acpi/acpica/tbutils.c | 184 +++++++++++++++++++++++--- drivers/acpi/acpica/tbxface.c | 101 +++++++++++++- drivers/acpi/osl.c | 252 ++++++++++++++++++++++++++++++++--- drivers/acpi/tables.c | 29 +++- include/acpi/acpixf.h | 8 + include/linux/acpi.h | 24 +++- include/linux/memblock.h | 13 ++ include/linux/memory_hotplug.h | 5 + lib/earlycpio.c | 27 ++-- mm/memblock.c | 92 +++++++++++-- mm/memory_hotplug.c | 104 ++++++++++++++- mm/page_alloc.c | 31 ++++- 19 files changed, 873 insertions(+), 125 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/