Hello tejun, Could you please help reviewing the patchset? As you suggested, we've make the patchset much simpler and cleaner. Thanks in advance! On 09/13/2013 05:30 PM, Tang Chen wrote: > This patch-set is based on tj's suggestion, and not fully tested. > Just for review and discussion. > > This patch-set is based on the latest kernel (3.11) > HEAD is: > commit d5d04bb48f0eb89c14e76779bb46212494de0bec > Author: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Date: Wed Sep 11 19:55:12 2013 -0700 > > > [Problem] > > The current Linux cannot migrate pages used by the kerenl because > of the kernel direct mapping. In Linux kernel space, va = pa + PAGE_OFFSET. > When the pa is changed, we cannot simply update the pagetable and > keep the va unmodified. So the kernel pages are not migratable. > > There are also some other issues will cause the kernel pages not migratable. > For example, the physical address may be cached somewhere and will be used. > It is not to update all the caches. > > When doing memory hotplug in Linux, we first migrate all the pages in one > memory device somewhere else, and then remove the device. But if pages are > used by the kernel, they are not migratable. As a result, memory used by > the kernel cannot be hot-removed. > > Modifying the kernel direct mapping mechanism is too difficult to do. And > it may cause the kernel performance down and unstable. So we use the following > way to do memory hotplug. > > > [What we are doing] > > In Linux, memory in one numa node is divided into several zones. One of the > zones is ZONE_MOVABLE, which the kernel won't use. > > In order to implement memory hotplug in Linux, we are going to arrange all > hotpluggable memory in ZONE_MOVABLE so that the kernel won't use these memory. > To do this, we need ACPI's help. > > In ACPI, SRAT(System Resource Affinity Table) contains NUMA info. The memory > affinities in SRAT record every memory range in the system, and also, flags > specifying if the memory range is hotpluggable. > (Please refer to ACPI spec 5.0 5.2.16) > > With the help of SRAT, we have to do the following two things to achieve our > goal: > > 1. When doing memory hot-add, allow the users arranging hotpluggable as > ZONE_MOVABLE. > (This has been done by the MOVABLE_NODE functionality in Linux.) > > 2. when the system is booting, prevent bootmem allocator from allocating > hotpluggable memory for the kernel before the memory initialization > finishes. > > The problem 2 is the key problem we are going to solve. But before solving it, > we need some preparation. Please see below. > > > [Preparation] > > Bootloader has to load the kernel image into memory. And this memory must be > unhotpluggable. We cannot prevent this anyway. So in a memory hotplug system, > we can assume any node the kernel resides in is not hotpluggable. > > Before SRAT is parsed, we don't know which memory ranges are hotpluggable. But > memblock has already started to work. In the current kernel, memblock allocates > the following memory before SRAT is parsed: > > setup_arch() > |->memblock_x86_fill() /* memblock is ready */ > |...... > |->early_reserve_e820_mpc_new() /* allocate memory under 1MB */ > |->reserve_real_mode() /* allocate memory under 1MB */ > |->init_mem_mapping() /* allocate page tables, about 2MB to map 1GB memory */ > |->dma_contiguous_reserve() /* specified by user, should be low */ > |->setup_log_buf() /* specified by user, several mega bytes */ > |->relocate_initrd() /* could be large, but will be freed after boot, should reorder */ > |->acpi_initrd_override() /* several mega bytes */ > |->reserve_crashkernel() /* could be large, should reorder */ > |...... > |->initmem_init() /* Parse SRAT */ > > According to Tejun's advice, before SRAT is parsed, we should try our best to > allocate memory near the kernel image. Since the whole node the kernel resides > in won't be hotpluggable, and for a modern server, a node may have at least 16GB > memory, allocating several mega bytes memory around the kernel image won't cross > to hotpluggable memory. > > > [About this patch-set] > > So this patch-set does the following: > > 1. Make memblock be able to allocate memory from low address to high address. > 1) Keep all the memblock APIs' prototype unmodified. > 2) When the direction is bottom up, keep the start address greater than the > end of kernel image. > > 2. Improve init_mem_mapping() to support allocate page tables in bottom up direction. > > 3. Introduce "movablenode" boot option to enable and disable this functionality. > > PS: Reordering of relocate_initrd() has not been done yet. acpi_initrd_override() > needs to access initrd with virtual address. So relocate_initrd() must be done > before acpi_initrd_override(). > > > Change log v2 -> v3: > 1. According to Toshi's suggestion, move the direction checking logic into memblock. > And simply the code more. > > Change log v1 -> v2: > 1. According to tj's suggestion, implemented a new function memblock_alloc_bottom_up() > to allocate memory from bottom upwards, whihc can simplify the code. > > > Tang Chen (5): > memblock: Introduce allocation direction to memblock. > memblock: Improve memblock to support allocation from lower address. > x86, acpi, crash, kdump: Do reserve_crashkernel() after SRAT is > parsed. > x86, mem-hotplug: Support initialize page tables from low to high. > mem-hotplug: Introduce movablenode boot option to control memblock > allocation direction. > > Documentation/kernel-parameters.txt | 15 ++++ > arch/x86/kernel/setup.c | 44 ++++++++++++- > arch/x86/mm/init.c | 121 ++++++++++++++++++++++++++-------- > include/linux/memblock.h | 22 ++++++ > include/linux/memory_hotplug.h | 5 ++ > mm/memblock.c | 120 +++++++++++++++++++++++++++++++---- > mm/memory_hotplug.c | 9 +++ > 7 files changed, 293 insertions(+), 43 deletions(-) > > -- Thanks. Zhang Yanfei -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>