From 1402899e43fda490f08d2c47a7558931f8b9c60c Mon Sep 17 00:00:00 2001 From: Tang Chen Date: Tue, 12 Nov 2013 15:07:57 -0800 Subject: mm/memblock.c: factor out of top-down allocation [Problem] The current Linux cannot migrate pages used by the kernel 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 patchset] So this patchset is the preparation for the problem 2 that we want to solve. It does the following: 1. Make memblock be able to allocate memory bottom up. 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 "movable_node" boot option to enable and disable this functionality. This patch (of 6): Create a new function __memblock_find_range_top_down to factor out of top-down allocation from memblock_find_in_range_node. This is a preparation because we will introduce a new bottom-up allocation mode in the following patch. Signed-off-by: Tang Chen Signed-off-by: Zhang Yanfei Acked-by: Tejun Heo Acked-by: Toshi Kani Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: Wanpeng Li Cc: Thomas Renninger Cc: Yinghai Lu Cc: Jiang Liu Cc: Wen Congyang Cc: Lai Jiangshan Cc: Yasuaki Ishimatsu Cc: Taku Izumi Cc: Mel Gorman Cc: Michal Nazarewicz Cc: Minchan Kim Cc: Rik van Riel Cc: Johannes Weiner Cc: Kamezawa Hiroyuki Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memblock.c | 47 ++++++++++++++++++++++++++++++++++------------- 1 file changed, 34 insertions(+), 13 deletions(-) (limited to 'mm/memblock.c') diff --git a/mm/memblock.c b/mm/memblock.c index 0ac412a0a7ee..accff1087137 100644 --- a/mm/memblock.c +++ b/mm/memblock.c @@ -83,33 +83,25 @@ static long __init_memblock memblock_overlaps_region(struct memblock_type *type, } /** - * memblock_find_in_range_node - find free area in given range and node + * __memblock_find_range_top_down - find free area utility, in top-down * @start: start of candidate range * @end: end of candidate range, can be %MEMBLOCK_ALLOC_{ANYWHERE|ACCESSIBLE} * @size: size of free area to find * @align: alignment of free area to find * @nid: nid of the free area to find, %MAX_NUMNODES for any node * - * Find @size free area aligned to @align in the specified range and node. + * Utility called from memblock_find_in_range_node(), find free area top-down. * * RETURNS: * Found address on success, %0 on failure. */ -phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t start, - phys_addr_t end, phys_addr_t size, - phys_addr_t align, int nid) +static phys_addr_t __init_memblock +__memblock_find_range_top_down(phys_addr_t start, phys_addr_t end, + phys_addr_t size, phys_addr_t align, int nid) { phys_addr_t this_start, this_end, cand; u64 i; - /* pump up @end */ - if (end == MEMBLOCK_ALLOC_ACCESSIBLE) - end = memblock.current_limit; - - /* avoid allocating the first page */ - start = max_t(phys_addr_t, start, PAGE_SIZE); - end = max(start, end); - for_each_free_mem_range_reverse(i, nid, &this_start, &this_end, NULL) { this_start = clamp(this_start, start, end); this_end = clamp(this_end, start, end); @@ -121,9 +113,38 @@ phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t start, if (cand >= this_start) return cand; } + return 0; } +/** + * memblock_find_in_range_node - find free area in given range and node + * @start: start of candidate range + * @end: end of candidate range, can be %MEMBLOCK_ALLOC_{ANYWHERE|ACCESSIBLE} + * @size: size of free area to find + * @align: alignment of free area to find + * @nid: nid of the free area to find, %MAX_NUMNODES for any node + * + * Find @size free area aligned to @align in the specified range and node. + * + * RETURNS: + * Found address on success, %0 on failure. + */ +phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t start, + phys_addr_t end, phys_addr_t size, + phys_addr_t align, int nid) +{ + /* pump up @end */ + if (end == MEMBLOCK_ALLOC_ACCESSIBLE) + end = memblock.current_limit; + + /* avoid allocating the first page */ + start = max_t(phys_addr_t, start, PAGE_SIZE); + end = max(start, end); + + return __memblock_find_range_top_down(start, end, size, align, nid); +} + /** * memblock_find_in_range - find free area in given range * @start: start of candidate range -- cgit v1.2.3 From 79442ed189acb8b949662676e750eda173c06f9b Mon Sep 17 00:00:00 2001 From: Tang Chen Date: Tue, 12 Nov 2013 15:07:59 -0800 Subject: mm/memblock.c: introduce bottom-up allocation mode The Linux kernel cannot migrate pages used by the kernel. As a result, kernel pages cannot be hot-removed. So we cannot allocate hotpluggable memory for the kernel. ACPI SRAT (System Resource Affinity Table) contains the memory hotplug info. But before SRAT is parsed, memblock has already started to allocate memory for the kernel. So we need to prevent memblock from doing this. In a memory hotplug system, any numa node the kernel resides in should be unhotpluggable. And for a modern server, each node could have at least 16GB memory. So memory around the kernel image is highly likely unhotpluggable. So the basic idea is: Allocate memory from the end of the kernel image and to the higher memory. Since memory allocation before SRAT is parsed won't be too much, it could highly likely be in the same node with kernel image. The current memblock can only allocate memory top-down. So this patch introduces a new bottom-up allocation mode to allocate memory bottom-up. And later when we use this allocation direction to allocate memory, we will limit the start address above the kernel. Signed-off-by: Tang Chen Signed-off-by: Zhang Yanfei Acked-by: Toshi Kani Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: Tejun Heo Cc: Wanpeng Li Cc: Thomas Renninger Cc: Yinghai Lu Cc: Jiang Liu Cc: Wen Congyang Cc: Lai Jiangshan Cc: Yasuaki Ishimatsu Cc: Taku Izumi Cc: Mel Gorman Cc: Michal Nazarewicz Cc: Minchan Kim Cc: Rik van Riel Cc: Johannes Weiner Cc: Kamezawa Hiroyuki Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/memblock.h | 24 ++++++++++++++ include/linux/mm.h | 4 +++ mm/memblock.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++-- 3 files changed, 108 insertions(+), 3 deletions(-) (limited to 'mm/memblock.c') diff --git a/include/linux/memblock.h b/include/linux/memblock.h index 31e95acddb4d..77c60e52939d 100644 --- a/include/linux/memblock.h +++ b/include/linux/memblock.h @@ -35,6 +35,7 @@ struct memblock_type { }; struct memblock { + bool bottom_up; /* is bottom up direction? */ phys_addr_t current_limit; struct memblock_type memory; struct memblock_type reserved; @@ -148,6 +149,29 @@ phys_addr_t memblock_alloc_try_nid(phys_addr_t size, phys_addr_t align, int nid) phys_addr_t memblock_alloc(phys_addr_t size, phys_addr_t align); +#ifdef CONFIG_MOVABLE_NODE +/* + * Set the allocation direction to bottom-up or top-down. + */ +static inline void memblock_set_bottom_up(bool enable) +{ + memblock.bottom_up = enable; +} + +/* + * Check if the allocation direction is bottom-up or not. + * if this is true, that said, memblock will allocate memory + * in bottom-up direction. + */ +static inline bool memblock_bottom_up(void) +{ + return memblock.bottom_up; +} +#else +static inline void memblock_set_bottom_up(bool enable) {} +static inline bool memblock_bottom_up(void) { return false; } +#endif + /* Flags for memblock_alloc_base() amd __memblock_alloc_base() */ #define MEMBLOCK_ALLOC_ANYWHERE (~(phys_addr_t)0) #define MEMBLOCK_ALLOC_ACCESSIBLE 0 diff --git a/include/linux/mm.h b/include/linux/mm.h index 8aa4006b9636..42a35d94b82c 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -50,6 +50,10 @@ extern int sysctl_legacy_va_layout; #include #include +#ifndef __pa_symbol +#define __pa_symbol(x) __pa(RELOC_HIDE((unsigned long)(x), 0)) +#endif + extern unsigned long sysctl_user_reserve_kbytes; extern unsigned long sysctl_admin_reserve_kbytes; diff --git a/mm/memblock.c b/mm/memblock.c index accff1087137..53e477bb5558 100644 --- a/mm/memblock.c +++ b/mm/memblock.c @@ -20,6 +20,8 @@ #include #include +#include + static struct memblock_region memblock_memory_init_regions[INIT_MEMBLOCK_REGIONS] __initdata_memblock; static struct memblock_region memblock_reserved_init_regions[INIT_MEMBLOCK_REGIONS] __initdata_memblock; @@ -32,6 +34,7 @@ struct memblock memblock __initdata_memblock = { .reserved.cnt = 1, /* empty dummy entry */ .reserved.max = INIT_MEMBLOCK_REGIONS, + .bottom_up = false, .current_limit = MEMBLOCK_ALLOC_ANYWHERE, }; @@ -82,6 +85,38 @@ static long __init_memblock memblock_overlaps_region(struct memblock_type *type, return (i < type->cnt) ? i : -1; } +/* + * __memblock_find_range_bottom_up - find free area utility in bottom-up + * @start: start of candidate range + * @end: end of candidate range, can be %MEMBLOCK_ALLOC_{ANYWHERE|ACCESSIBLE} + * @size: size of free area to find + * @align: alignment of free area to find + * @nid: nid of the free area to find, %MAX_NUMNODES for any node + * + * Utility called from memblock_find_in_range_node(), find free area bottom-up. + * + * RETURNS: + * Found address on success, 0 on failure. + */ +static phys_addr_t __init_memblock +__memblock_find_range_bottom_up(phys_addr_t start, phys_addr_t end, + phys_addr_t size, phys_addr_t align, int nid) +{ + phys_addr_t this_start, this_end, cand; + u64 i; + + for_each_free_mem_range(i, nid, &this_start, &this_end, NULL) { + this_start = clamp(this_start, start, end); + this_end = clamp(this_end, start, end); + + cand = round_up(this_start, align); + if (cand < this_end && this_end - cand >= size) + return cand; + } + + return 0; +} + /** * __memblock_find_range_top_down - find free area utility, in top-down * @start: start of candidate range @@ -93,7 +128,7 @@ static long __init_memblock memblock_overlaps_region(struct memblock_type *type, * Utility called from memblock_find_in_range_node(), find free area top-down. * * RETURNS: - * Found address on success, %0 on failure. + * Found address on success, 0 on failure. */ static phys_addr_t __init_memblock __memblock_find_range_top_down(phys_addr_t start, phys_addr_t end, @@ -127,13 +162,24 @@ __memblock_find_range_top_down(phys_addr_t start, phys_addr_t end, * * Find @size free area aligned to @align in the specified range and node. * + * When allocation direction is bottom-up, the @start should be greater + * than the end of the kernel image. Otherwise, it will be trimmed. The + * reason is that we want the bottom-up allocation just near the kernel + * image so it is highly likely that the allocated memory and the kernel + * will reside in the same node. + * + * If bottom-up allocation failed, will try to allocate memory top-down. + * * RETURNS: - * Found address on success, %0 on failure. + * Found address on success, 0 on failure. */ phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t start, phys_addr_t end, phys_addr_t size, phys_addr_t align, int nid) { + int ret; + phys_addr_t kernel_end; + /* pump up @end */ if (end == MEMBLOCK_ALLOC_ACCESSIBLE) end = memblock.current_limit; @@ -141,6 +187,37 @@ phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t start, /* avoid allocating the first page */ start = max_t(phys_addr_t, start, PAGE_SIZE); end = max(start, end); + kernel_end = __pa_symbol(_end); + + /* + * try bottom-up allocation only when bottom-up mode + * is set and @end is above the kernel image. + */ + if (memblock_bottom_up() && end > kernel_end) { + phys_addr_t bottom_up_start; + + /* make sure we will allocate above the kernel */ + bottom_up_start = max(start, kernel_end); + + /* ok, try bottom-up allocation first */ + ret = __memblock_find_range_bottom_up(bottom_up_start, end, + size, align, nid); + if (ret) + return ret; + + /* + * we always limit bottom-up allocation above the kernel, + * but top-down allocation doesn't have the limit, so + * retrying top-down allocation may succeed when bottom-up + * allocation failed. + * + * bottom-up allocation is expected to be fail very rarely, + * so we use WARN_ONCE() here to see the stack trace if + * fail happens. + */ + WARN_ONCE(1, "memblock: bottom-up allocation failed, " + "memory hotunplug may be affected\n"); + } return __memblock_find_range_top_down(start, end, size, align, nid); } @@ -155,7 +232,7 @@ phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t start, * Find @size free area aligned to @align in the specified range. * * RETURNS: - * Found address on success, %0 on failure. + * Found address on success, 0 on failure. */ phys_addr_t __init_memblock memblock_find_in_range(phys_addr_t start, phys_addr_t end, phys_addr_t size, -- cgit v1.2.3