English

Chinese (Simplified)

Boot time memory management¶

Early system initialization cannot use “normal” memory management simply because it is not set up yet. But there is still need to allocate memory for various data structures, for instance for the physical page allocator.

A specialized allocator called memblock performs the boot time memory management. The architecture specific initialization must set it up in setup_arch() and tear it down in mem_init() functions.

Once the early memory management is available it offers a variety of functions and macros for memory allocations. The allocation request may be directed to the first (and probably the only) node or to a particular node in a NUMA system. There are API variants that panic when an allocation fails and those that don’t.

Memblock also offers a variety of APIs that control its own behaviour.

Memblock Overview¶

Memblock is a method of managing memory regions during the early boot period when the usual kernel memory allocators are not up and running.

Memblock views the system memory as collections of contiguous regions. There are several types of these collections:

memory - describes the physical memory available to the kernel; this may differ from the actual physical memory installed in the system, for instance when the memory is restricted with mem= command line parameter
reserved - describes the regions that were allocated
physmem - describes the actual physical memory available during boot regardless of the possible restrictions and memory hot(un)plug; the physmem type is only available on some architectures.

Each region is represented by struct memblock_region that defines the region extents, its attributes and NUMA node id on NUMA systems. Every memory type is described by the struct memblock_type which contains an array of memory regions along with the allocator metadata. The “memory” and “reserved” types are nicely wrapped with struct memblock. This structure is statically initialized at build time. The region arrays are initially sized to INIT_MEMBLOCK_MEMORY_REGIONS for “memory” and INIT_MEMBLOCK_RESERVED_REGIONS for “reserved”. The region array for “physmem” is initially sized to INIT_PHYSMEM_REGIONS. The memblock_allow_resize() enables automatic resizing of the region arrays during addition of new regions. This feature should be used with care so that memory allocated for the region array will not overlap with areas that should be reserved, for example initrd.

The early architecture setup should tell memblock what the physical memory layout is by using memblock_add() or memblock_add_node() functions. The first function does not assign the region to a NUMA node and it is appropriate for UMA systems. Yet, it is possible to use it on NUMA systems as well and assign the region to a NUMA node later in the setup process using memblock_set_node(). The memblock_add_node() performs such an assignment directly.

Once memblock is setup the memory can be allocated using one of the API variants:

memblock_phys_alloc*() - these functions return the physical address of the allocated memory
memblock_alloc*() - these functions return the virtual address of the allocated memory.

Note, that both API variants use implicit assumptions about allowed memory ranges and the fallback methods. Consult the documentation of memblock_alloc_internal() and memblock_alloc_range_nid() functions for more elaborate description.

As the system boot progresses, the architecture specific mem_init() function frees all the memory to the buddy page allocator.

Unless an architecture enables CONFIG_ARCH_KEEP_MEMBLOCK, the memblock data structures (except “physmem”) will be discarded after the system initialization completes.

Functions and structures¶

Here is the description of memblock data structures, functions and macros. Some of them are actually internal, but since they are documented it would be silly to omit them. Besides, reading the descriptions for the internal functions can help to understand what really happens under the hood.

enum memblock_flags¶: definition of memory region attributes

Constants

MEMBLOCK_NONE: no special request
MEMBLOCK_HOTPLUG: memory region indicated in the firmware-provided memory map during early boot as hot(un)pluggable system RAM (e.g., memory range that might get hotunplugged later). With “movable_node” set on the kernel commandline, try keeping this memory region hotunpluggable. Does not apply to memblocks added (“hotplugged”) after early boot.
MEMBLOCK_MIRROR: mirrored region
MEMBLOCK_NOMAP: don’t add to kernel direct mapping and treat as reserved in the memory map; refer to memblock_mark_nomap() description for further details
MEMBLOCK_DRIVER_MANAGED: memory region that is always detected and added via a driver, and never indicated in the firmware-provided memory map as system RAM. This corresponds to IORESOURCE_SYSRAM_DRIVER_MANAGED in the kernel resource tree.
MEMBLOCK_RSRV_NOINIT: memory region for which struct pages are not initialized (only for reserved regions).

struct memblock_region¶: represents a memory region

Definition:

struct memblock_region {
    phys_addr_t base;
    phys_addr_t size;
    enum memblock_flags flags;
#ifdef CONFIG_NUMA;
    int nid;
#endif;
};

Members

base: base address of the region
size: size of the region
flags: memory region attributes
nid: NUMA node id

struct memblock_type¶: collection of memory regions of certain type

Definition:

struct memblock_type {
    unsigned long cnt;
    unsigned long max;
    phys_addr_t total_size;
    struct memblock_region *regions;
    char *name;
};

Members

cnt: number of regions
max: size of the allocated array
total_size: size of all regions
regions: array of regions
name: the memory type symbolic name

struct memblock¶: memblock allocator metadata

Definition:

struct memblock {
    bool bottom_up;
    phys_addr_t current_limit;
    struct memblock_type memory;
    struct memblock_type reserved;
};

Members

bottom_up: is bottom up direction?
current_limit: physical address of the current allocation limit
memory: usable memory regions
reserved: reserved memory regions

for_each_physmem_range¶

for_each_physmem_range (i, type, p_start, p_end)

iterate through physmem areas not included in type.

Parameters

i: u64 used as loop variable
type: ptr to memblock_type which excludes from the iteration, can be NULL
p_start: ptr to phys_addr_t for start address of the range, can be NULL
p_end: ptr to phys_addr_t for end address of the range, can be NULL

__for_each_mem_range¶

__for_each_mem_range (i, type_a, type_b, nid, flags, p_start, p_end, p_nid)

iterate through memblock areas from type_a and not included in type_b. Or just type_a if type_b is NULL.

Parameters

i: u64 used as loop variable
type_a: ptr to memblock_type to iterate
type_b: ptr to memblock_type which excludes from the iteration
nid: node selector, NUMA_NO_NODE for all nodes
flags: pick from blocks based on memory attributes
p_start: ptr to phys_addr_t for start address of the range, can be NULL
p_end: ptr to phys_addr_t for end address of the range, can be NULL
p_nid: ptr to int for nid of the range, can be NULL

__for_each_mem_range_rev¶

__for_each_mem_range_rev (i, type_a, type_b, nid, flags, p_start, p_end, p_nid)

reverse iterate through memblock areas from type_a and not included in type_b. Or just type_a if type_b is NULL.

Parameters

i: u64 used as loop variable
type_a: ptr to memblock_type to iterate
type_b: ptr to memblock_type which excludes from the iteration
nid: node selector, NUMA_NO_NODE for all nodes
flags: pick from blocks based on memory attributes
p_start: ptr to phys_addr_t for start address of the range, can be NULL
p_end: ptr to phys_addr_t for end address of the range, can be NULL
p_nid: ptr to int for nid of the range, can be NULL

for_each_mem_range¶

for_each_mem_range (i, p_start, p_end)

iterate through memory areas.

Parameters

i: u64 used as loop variable
p_start: ptr to phys_addr_t for start address of the range, can be NULL
p_end: ptr to phys_addr_t for end address of the range, can be NULL

for_each_mem_range_rev¶

for_each_mem_range_rev (i, p_start, p_end)

reverse iterate through memblock areas from type_a and not included in type_b. Or just type_a if type_b is NULL.

Parameters

i: u64 used as loop variable
p_start: ptr to phys_addr_t for start address of the range, can be NULL
p_end: ptr to phys_addr_t for end address of the range, can be NULL

for_each_reserved_mem_range¶

for_each_reserved_mem_range (i, p_start, p_end)

iterate over all reserved memblock areas

Parameters

i: u64 used as loop variable
p_start: ptr to phys_addr_t for start address of the range, can be NULL
p_end: ptr to phys_addr_t for end address of the range, can be NULL

Description

Walks over reserved areas of memblock. Available as soon as memblock is initialized.

for_each_mem_pfn_range¶

for_each_mem_pfn_range (i, nid, p_start, p_end, p_nid)

early memory pfn range iterator

Parameters

i: an integer used as loop variable
nid: node selector, MAX_NUMNODES for all nodes
p_start: ptr to ulong for start pfn of the range, can be NULL
p_end: ptr to ulong for end pfn of the range, can be NULL
p_nid: ptr to int for nid of the range, can be NULL

Description

Walks over configured memory ranges.

for_each_free_mem_pfn_range_in_zone_from¶

for_each_free_mem_pfn_range_in_zone_from (i, zone, p_start, p_end)

iterate through zone specific free memblock areas from a given point

Parameters

i: u64 used as loop variable
zone: zone in which all of the memory blocks reside
p_start: ptr to phys_addr_t for start address of the range, can be NULL
p_end: ptr to phys_addr_t for end address of the range, can be NULL

Description

Walks over free (memory && !reserved) areas of memblock in a specific zone, continuing from current position. Available as soon as memblock is initialized.

for_each_free_mem_range¶

for_each_free_mem_range (i, nid, flags, p_start, p_end, p_nid)

iterate through free memblock areas

Parameters

i: u64 used as loop variable
nid: node selector, NUMA_NO_NODE for all nodes
flags: pick from blocks based on memory attributes
p_start: ptr to phys_addr_t for start address of the range, can be NULL
p_end: ptr to phys_addr_t for end address of the range, can be NULL
p_nid: ptr to int for nid of the range, can be NULL

Description

Walks over free (memory && !reserved) areas of memblock. Available as soon as memblock is initialized.

for_each_free_mem_range_reverse¶

for_each_free_mem_range_reverse (i, nid, flags, p_start, p_end, p_nid)

rev-iterate through free memblock areas

Parameters

i: u64 used as loop variable
nid: node selector, NUMA_NO_NODE for all nodes
flags: pick from blocks based on memory attributes
p_start: ptr to phys_addr_t for start address of the range, can be NULL
p_end: ptr to phys_addr_t for end address of the range, can be NULL
p_nid: ptr to int for nid of the range, can be NULL

Description

Walks over free (memory && !reserved) areas of memblock in reverse order. Available as soon as memblock is initialized.

void memblock_set_current_limit(phys_addr_t limit)¶: Set the current allocation limit to allow limiting allocations to what is currently accessible during boot

Parameters

phys_addr_t limit: New limit value (physical address)

unsigned long memblock_region_memory_base_pfn(const struct memblock_region *reg)¶: get the lowest pfn of the memory region

Parameters

const struct memblock_region *reg: memblock_region structure

Return

the lowest pfn intersecting with the memory region

unsigned long memblock_region_memory_end_pfn(const struct memblock_region *reg)¶: get the end pfn of the memory region

Parameters

const struct memblock_region *reg: memblock_region structure

Return

the end_pfn of the reserved region

unsigned long memblock_region_reserved_base_pfn(const struct memblock_region *reg)¶: get the lowest pfn of the reserved region

Parameters

const struct memblock_region *reg: memblock_region structure

Return

the lowest pfn intersecting with the reserved region

unsigned long memblock_region_reserved_end_pfn(const struct memblock_region *reg)¶: get the end pfn of the reserved region

Parameters

const struct memblock_region *reg: memblock_region structure

Return

the end_pfn of the reserved region

for_each_mem_region¶

for_each_mem_region (region)

iterate over memory regions

Parameters

region: loop variable

for_each_reserved_mem_region¶

for_each_reserved_mem_region (region)

itereate over reserved memory regions

Parameters

region: loop variable

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, enum memblock_flags flags)¶: find free area utility in bottom-up

Parameters

phys_addr_t start: start of candidate range
phys_addr_t end: end of candidate range, can be MEMBLOCK_ALLOC_ANYWHERE or MEMBLOCK_ALLOC_ACCESSIBLE
phys_addr_t size: size of free area to find
phys_addr_t align: alignment of free area to find
int nid: nid of the free area to find, NUMA_NO_NODE for any node
enum memblock_flags flags: pick from blocks based on memory attributes

Description

Utility called from memblock_find_in_range_node(), find free area bottom-up.

Return

Found address on success, 0 on failure.

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, enum memblock_flags flags)¶: find free area utility, in top-down

Parameters

phys_addr_t start: start of candidate range
phys_addr_t end: end of candidate range, can be MEMBLOCK_ALLOC_ANYWHERE or MEMBLOCK_ALLOC_ACCESSIBLE
phys_addr_t size: size of free area to find
phys_addr_t align: alignment of free area to find
int nid: nid of the free area to find, NUMA_NO_NODE for any node
enum memblock_flags flags: pick from blocks based on memory attributes

Description

Utility called from memblock_find_in_range_node(), find free area top-down.

Return

Found address on success, 0 on failure.

phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t size, phys_addr_t align, phys_addr_t start, phys_addr_t end, int nid, enum memblock_flags flags)¶: find free area in given range and node

Parameters

phys_addr_t size: size of free area to find
phys_addr_t align: alignment of free area to find
phys_addr_t start: start of candidate range
phys_addr_t end: end of candidate range, can be MEMBLOCK_ALLOC_ANYWHERE or MEMBLOCK_ALLOC_ACCESSIBLE
int nid: nid of the free area to find, NUMA_NO_NODE for any node
enum memblock_flags flags: pick from blocks based on memory attributes

Description

Find size free area aligned to align in the specified range and node.

Return

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, phys_addr_t align)¶: find free area in given range

Parameters

phys_addr_t start: start of candidate range
phys_addr_t end: end of candidate range, can be MEMBLOCK_ALLOC_ANYWHERE or MEMBLOCK_ALLOC_ACCESSIBLE
phys_addr_t size: size of free area to find
phys_addr_t align: alignment of free area to find

Description

Find size free area aligned to align in the specified range.

Return

Found address on success, 0 on failure.

void memblock_discard(void)¶: discard memory and reserved arrays if they were allocated

Parameters

void: no arguments

int __init_memblock memblock_double_array(struct memblock_type *type, phys_addr_t new_area_start, phys_addr_t new_area_size)¶: double the size of the memblock regions array

Parameters

struct memblock_type *type: memblock type of the regions array being doubled
phys_addr_t new_area_start: starting address of memory range to avoid overlap with
phys_addr_t new_area_size: size of memory range to avoid overlap with

Description

Double the size of the type regions array. If memblock is being used to allocate memory for a new reserved regions array and there is a previously allocated memory range [new_area_start, new_area_start + new_area_size] waiting to be reserved, ensure the memory used by the new array does not overlap.

Return

0 on success, -1 on failure.

void __init_memblock memblock_merge_regions(struct memblock_type *type, unsigned long start_rgn, unsigned long end_rgn)¶: merge neighboring compatible regions

Parameters

struct memblock_type *type: memblock type to scan
unsigned long start_rgn: start scanning from (start_rgn - 1)
unsigned long end_rgn: end scanning at (end_rgn - 1) Scan type and merge neighboring compatible regions in [start_rgn - 1, end_rgn)

void __init_memblock memblock_insert_region(struct memblock_type *type, int idx, phys_addr_t base, phys_addr_t size, int nid, enum memblock_flags flags)¶: insert new memblock region

Parameters

struct memblock_type *type: memblock type to insert into
int idx: index for the insertion point
phys_addr_t base: base address of the new region
phys_addr_t size: size of the new region
int nid: node id of the new region
enum memblock_flags flags: flags of the new region

Description

Insert new memblock region [base, base + size) into type at idx. type must already have extra room to accommodate the new region.

int __init_memblock memblock_add_range(struct memblock_type *type, phys_addr_t base, phys_addr_t size, int nid, enum memblock_flags flags)¶: add new memblock region

Parameters

struct memblock_type *type: memblock type to add new region into
phys_addr_t base: base address of the new region
phys_addr_t size: size of the new region
int nid: nid of the new region
enum memblock_flags flags: flags of the new region

Description

Add new memblock region [base, base + size) into type. The new region is allowed to overlap with existing ones - overlaps don’t affect already existing regions. type is guaranteed to be minimal (all neighbouring compatible regions are merged) after the addition.

Return

0 on success, -errno on failure.

int __init_memblock memblock_add_node(phys_addr_t base, phys_addr_t size, int nid, enum memblock_flags flags)¶: add new memblock region within a NUMA node

Parameters

phys_addr_t base: base address of the new region
phys_addr_t size: size of the new region
int nid: nid of the new region
enum memblock_flags flags: flags of the new region

Description

Add new memblock region [base, base + size) to the “memory” type. See memblock_add_range() description for mode details

Return

0 on success, -errno on failure.

int __init_memblock memblock_add(phys_addr_t base, phys_addr_t size)¶: add new memblock region

Parameters

phys_addr_t base: base address of the new region
phys_addr_t size: size of the new region

Description

Add new memblock region [base, base + size) to the “memory” type. See memblock_add_range() description for mode details

Return

0 on success, -errno on failure.

bool __init_memblock memblock_validate_numa_coverage(unsigned long threshold_bytes)¶: check if amount of memory with no node ID assigned is less than a threshold

Parameters

unsigned long threshold_bytes: maximal memory size that can have unassigned node ID (in bytes).

Description

A buggy firmware may report memory that does not belong to any node. Check if amount of such memory is below threshold_bytes.

Return

true on success, false on failure.

int __init_memblock memblock_isolate_range(struct memblock_type *type, phys_addr_t base, phys_addr_t size, int *start_rgn, int *end_rgn)¶: isolate given range into disjoint memblocks

Parameters

struct memblock_type *type: memblock type to isolate range for
phys_addr_t base: base of range to isolate
phys_addr_t size: size of range to isolate
int *start_rgn: out parameter for the start of isolated region
int *end_rgn: out parameter for the end of isolated region

Description

Walk type and ensure that regions don’t cross the boundaries defined by [base, base + size). Crossing regions are split at the boundaries, which may create at most two more regions. The index of the first region inside the range is returned in *start_rgn and the index of the first region after the range is returned in *end_rgn.

Return

0 on success, -errno on failure.

void __init_memblock memblock_free(void *ptr, size_t size)¶: free boot memory allocation

Parameters

void *ptr: starting address of the boot memory allocation
size_t size: size of the boot memory block in bytes

Description

Free boot memory block previously allocated by memblock_alloc_xx() API. The freeing memory will not be released to the buddy allocator.

int __init_memblock memblock_phys_free(phys_addr_t base, phys_addr_t size)¶: free boot memory block

Parameters

phys_addr_t base: phys starting address of the boot memory block
phys_addr_t size: size of the boot memory block in bytes

Description

Free boot memory block previously allocated by memblock_phys_alloc_xx() API. The freeing memory will not be released to the buddy allocator.

int __init_memblock memblock_setclr_flag(struct memblock_type *type, phys_addr_t base, phys_addr_t size, int set, int flag)¶: set or clear flag for a memory region

Parameters

struct memblock_type *type: memblock type to set/clear flag for
phys_addr_t base: base address of the region
phys_addr_t size: size of the region
int set: set or clear the flag
int flag: the flag to update

Description

This function isolates region [base, base + size), and sets/clears flag

Return

0 on success, -errno on failure.

int __init_memblock memblock_mark_hotplug(phys_addr_t base, phys_addr_t size)¶: Mark hotpluggable memory with flag MEMBLOCK_HOTPLUG.

Parameters

phys_addr_t base: the base phys addr of the region
phys_addr_t size: the size of the region

Return

0 on success, -errno on failure.

int __init_memblock memblock_clear_hotplug(phys_addr_t base, phys_addr_t size)¶: Clear flag MEMBLOCK_HOTPLUG for a specified region.

Parameters

phys_addr_t base: the base phys addr of the region
phys_addr_t size: the size of the region

Return

0 on success, -errno on failure.

int __init_memblock memblock_mark_mirror(phys_addr_t base, phys_addr_t size)¶: Mark mirrored memory with flag MEMBLOCK_MIRROR.

Parameters

phys_addr_t base: the base phys addr of the region
phys_addr_t size: the size of the region

Return

0 on success, -errno on failure.

int __init_memblock memblock_mark_nomap(phys_addr_t base, phys_addr_t size)¶: Mark a memory region with flag MEMBLOCK_NOMAP.

Parameters

phys_addr_t base: the base phys addr of the region
phys_addr_t size: the size of the region

Description

The memory regions marked with MEMBLOCK_NOMAP will not be added to the direct mapping of the physical memory. These regions will still be covered by the memory map. The struct page representing NOMAP memory frames in the memory map will be PageReserved()

Note

if the memory being marked MEMBLOCK_NOMAP was allocated from memblock, the caller must inform kmemleak to ignore that memory

Return

0 on success, -errno on failure.

int __init_memblock memblock_clear_nomap(phys_addr_t base, phys_addr_t size)¶: Clear flag MEMBLOCK_NOMAP for a specified region.

Parameters

phys_addr_t base: the base phys addr of the region
phys_addr_t size: the size of the region

Return

0 on success, -errno on failure.

int __init_memblock memblock_reserved_mark_noinit(phys_addr_t base, phys_addr_t size)¶: Mark a reserved memory region with flag MEMBLOCK_RSRV_NOINIT which results in the struct pages not being initialized for this region.

Parameters

phys_addr_t base: the base phys addr of the region
phys_addr_t size: the size of the region

Description

struct pages will not be initialized for reserved memory regions marked with MEMBLOCK_RSRV_NOINIT.

Return

0 on success, -errno on failure.

void __next_mem_range(u64 *idx, int nid, enum memblock_flags flags, struct memblock_type *type_a, struct memblock_type *type_b, phys_addr_t *out_start, phys_addr_t *out_end, int *out_nid)¶: next function for for_each_free_mem_range() etc.

Parameters

u64 *idx: pointer to u64 loop variable
int nid: node selector, NUMA_NO_NODE for all nodes
enum memblock_flags flags: pick from blocks based on memory attributes
struct memblock_type *type_a: pointer to memblock_type from where the range is taken
struct memblock_type *type_b: pointer to memblock_type which excludes memory from being taken
phys_addr_t *out_start: ptr to phys_addr_t for start address of the range, can be NULL
phys_addr_t *out_end: ptr to phys_addr_t for end address of the range, can be NULL
int *out_nid: ptr to int for nid of the range, can be NULL

Description

Find the first area from *idx which matches nid, fill the out parameters, and update *idx for the next iteration. The lower 32bit of *idx contains index into type_a and the upper 32bit indexes the areas before each region in type_b. For example, if type_b regions look like the following,

0:[0-16), 1:[32-48), 2:[128-130)

The upper 32bit indexes the following regions.

0:[0-0), 1:[16-32), 2:[48-128), 3:[130-MAX)

As both region arrays are sorted, the function advances the two indices in lockstep and returns each intersection.

void __init_memblock __next_mem_range_rev(u64 *idx, int nid, enum memblock_flags flags, struct memblock_type *type_a, struct memblock_type *type_b, phys_addr_t *out_start, phys_addr_t *out_end, int *out_nid)¶: generic next function for for_each_*_range_rev()

Parameters

u64 *idx: pointer to u64 loop variable
int nid: node selector, NUMA_NO_NODE for all nodes
enum memblock_flags flags: pick from blocks based on memory attributes
struct memblock_type *type_a: pointer to memblock_type from where the range is taken
struct memblock_type *type_b: pointer to memblock_type which excludes memory from being taken
phys_addr_t *out_start: ptr to phys_addr_t for start address of the range, can be NULL
phys_addr_t *out_end: ptr to phys_addr_t for end address of the range, can be NULL
int *out_nid: ptr to int for nid of the range, can be NULL

Description

Finds the next range from type_a which is not marked as unsuitable in type_b.

Reverse of __next_mem_range().

int __init_memblock memblock_set_node(phys_addr_t base, phys_addr_t size, struct memblock_type *type, int nid)¶: set node ID on memblock regions

Parameters

phys_addr_t base: base of area to set node ID for
phys_addr_t size: size of area to set node ID for
struct memblock_type *type: memblock type to set node ID for
int nid: node ID to set

Description

Set the nid of memblock type regions in [base, base + size) to nid. Regions which cross the area boundaries are split as necessary.

Return

0 on success, -errno on failure.

void __init_memblock __next_mem_pfn_range_in_zone(u64 *idx, struct zone *zone, unsigned long *out_spfn, unsigned long *out_epfn)¶: iterator for for_each_*_range_in_zone()

Parameters

u64 *idx: pointer to u64 loop variable
struct zone *zone: zone in which all of the memory blocks reside
unsigned long *out_spfn: ptr to ulong for start pfn of the range, can be NULL
unsigned long *out_epfn: ptr to ulong for end pfn of the range, can be NULL

Description

This function is meant to be a zone/pfn specific wrapper for the for_each_mem_range type iterators. Specifically they are used in the deferred memory init routines and as such we were duplicating much of this logic throughout the code. So instead of having it in multiple locations it seemed like it would make more sense to centralize this to one new iterator that does everything they need.

phys_addr_t memblock_alloc_range_nid(phys_addr_t size, phys_addr_t align, phys_addr_t start, phys_addr_t end, int nid, bool exact_nid)¶: allocate boot memory block

Parameters

phys_addr_t size: size of memory block to be allocated in bytes
phys_addr_t align: alignment of the region and block’s size
phys_addr_t start: the lower bound of the memory region to allocate (phys address)
phys_addr_t end: the upper bound of the memory region to allocate (phys address)
int nid: nid of the free area to find, NUMA_NO_NODE for any node
bool exact_nid: control the allocation fall back to other nodes

Description

The allocation is performed from memory region limited by memblock.current_limit if end == MEMBLOCK_ALLOC_ACCESSIBLE.

If the specified node can not hold the requested memory and exact_nid is false, the allocation falls back to any node in the system.

For systems with memory mirroring, the allocation is attempted first from the regions with mirroring enabled and then retried from any memory region.

In addition, function using kmemleak_alloc_phys for allocated boot memory block, it is never reported as leaks.

Return

Physical address of allocated memory block on success, 0 on failure.

phys_addr_t memblock_phys_alloc_range(phys_addr_t size, phys_addr_t align, phys_addr_t start, phys_addr_t end)¶: allocate a memory block inside specified range

Parameters

phys_addr_t size: size of memory block to be allocated in bytes
phys_addr_t align: alignment of the region and block’s size
phys_addr_t start: the lower bound of the memory region to allocate (physical address)
phys_addr_t end: the upper bound of the memory region to allocate (physical address)

Description

Allocate size bytes in the between start and end.

Return

physical address of the allocated memory block on success, 0 on failure.

phys_addr_t memblock_phys_alloc_try_nid(phys_addr_t size, phys_addr_t align, int nid)¶: allocate a memory block from specified NUMA node

Parameters

phys_addr_t size: size of memory block to be allocated in bytes
phys_addr_t align: alignment of the region and block’s size
int nid: nid of the free area to find, NUMA_NO_NODE for any node

Description

Allocates memory block from the specified NUMA node. If the node has no available memory, attempts to allocated from any node in the system.

Return

physical address of the allocated memory block on success, 0 on failure.

void *memblock_alloc_internal(phys_addr_t size, phys_addr_t align, phys_addr_t min_addr, phys_addr_t max_addr, int nid, bool exact_nid)¶: allocate boot memory block

Parameters

phys_addr_t size: size of memory block to be allocated in bytes
phys_addr_t align: alignment of the region and block’s size
phys_addr_t min_addr: the lower bound of the memory region to allocate (phys address)
phys_addr_t max_addr: the upper bound of the memory region to allocate (phys address)
int nid: nid of the free area to find, NUMA_NO_NODE for any node
bool exact_nid: control the allocation fall back to other nodes

Description

Allocates memory block using memblock_alloc_range_nid() and converts the returned physical address to virtual.

The min_addr limit is dropped if it can not be satisfied and the allocation will fall back to memory below min_addr. Other constraints, such as node and mirrored memory will be handled again in memblock_alloc_range_nid().

Return

Virtual address of allocated memory block on success, NULL on failure.

void *memblock_alloc_exact_nid_raw(phys_addr_t size, phys_addr_t align, phys_addr_t min_addr, phys_addr_t max_addr, int nid)¶: allocate boot memory block on the exact node without zeroing memory

Parameters

phys_addr_t size: size of memory block to be allocated in bytes
phys_addr_t align: alignment of the region and block’s size
phys_addr_t min_addr: the lower bound of the memory region from where the allocation is preferred (phys address)
phys_addr_t max_addr: the upper bound of the memory region from where the allocation is preferred (phys address), or MEMBLOCK_ALLOC_ACCESSIBLE to allocate only from memory limited by memblock.current_limit value
int nid: nid of the free area to find, NUMA_NO_NODE for any node

Description

Public function, provides additional debug information (including caller info), if enabled. Does not zero allocated memory.

Return

Virtual address of allocated memory block on success, NULL on failure.

void *memblock_alloc_try_nid_raw(phys_addr_t size, phys_addr_t align, phys_addr_t min_addr, phys_addr_t max_addr, int nid)¶: allocate boot memory block without zeroing memory and without panicking

Parameters

phys_addr_t size: size of memory block to be allocated in bytes
phys_addr_t align: alignment of the region and block’s size
phys_addr_t min_addr: the lower bound of the memory region from where the allocation is preferred (phys address)
phys_addr_t max_addr: the upper bound of the memory region from where the allocation is preferred (phys address), or MEMBLOCK_ALLOC_ACCESSIBLE to allocate only from memory limited by memblock.current_limit value
int nid: nid of the free area to find, NUMA_NO_NODE for any node

Description

Public function, provides additional debug information (including caller info), if enabled. Does not zero allocated memory, does not panic if request cannot be satisfied.

Return

Virtual address of allocated memory block on success, NULL on failure.

void *memblock_alloc_try_nid(phys_addr_t size, phys_addr_t align, phys_addr_t min_addr, phys_addr_t max_addr, int nid)¶: allocate boot memory block

Parameters

phys_addr_t size: size of memory block to be allocated in bytes
phys_addr_t align: alignment of the region and block’s size
phys_addr_t min_addr: the lower bound of the memory region from where the allocation is preferred (phys address)
phys_addr_t max_addr: the upper bound of the memory region from where the allocation is preferred (phys address), or MEMBLOCK_ALLOC_ACCESSIBLE to allocate only from memory limited by memblock.current_limit value
int nid: nid of the free area to find, NUMA_NO_NODE for any node

Description

Public function, provides additional debug information (including caller info), if enabled. This function zeroes the allocated memory.

Return

Virtual address of allocated memory block on success, NULL on failure.

void memblock_free_late(phys_addr_t base, phys_addr_t size)¶: free pages directly to buddy allocator

Parameters

phys_addr_t base: phys starting address of the boot memory block
phys_addr_t size: size of the boot memory block in bytes

Description

This is only useful when the memblock allocator has already been torn down, but we are still initializing the system. Pages are released directly to the buddy allocator.

unsigned long memblock_estimated_nr_free_pages(void)¶: return estimated number of free pages from memblock point of view

Parameters

void: no arguments

Description

During bootup, subsystems might need a rough estimate of the number of free pages in the whole system, before precise numbers are available from the buddy. Especially with CONFIG_DEFERRED_STRUCT_PAGE_INIT, the numbers obtained from the buddy might be very imprecise during bootup.

Return

An estimated number of free pages from memblock point of view.

bool __init_memblock memblock_is_region_memory(phys_addr_t base, phys_addr_t size)¶: check if a region is a subset of memory

Parameters

phys_addr_t base: base of region to check
phys_addr_t size: size of region to check

Description

Check if the region [base, base + size) is a subset of a memory block.

Return

0 if false, non-zero if true

bool __init_memblock memblock_is_region_reserved(phys_addr_t base, phys_addr_t size)¶: check if a region intersects reserved memory

Parameters

phys_addr_t base: base of region to check
phys_addr_t size: size of region to check

Description

Check if the region [base, base + size) intersects a reserved memory block.

Return

True if they intersect, false if not.

void memblock_free_all(void)¶: release free pages to the buddy allocator

Parameters

void: no arguments

int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size)¶: Find reserved memory region with a given name

Parameters

const char *name: The name that is attached to a reserved memory region
phys_addr_t *start: If found, holds the start address
phys_addr_t *size: If found, holds the size of the address.

Description

start and size are only updated if name is found.

Return

1 if found or 0 if not found.

The Linux Kernel

Contents

This Page

Boot time memory management¶

Memblock Overview¶

Functions and structures¶