[Linux kernel memory management] Partition partner allocator ① (Partition partner allocator source code data structure | free_area free area array | MAX_ORDER macro definition | maximum page order of free area)

1. Partition partner allocator

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in the first two blogs

• [Linux Kernel Memory Management] Partner Allocator ① (Partner Allocator Introduction | Page Block, Order | Partner)
• [Linux Kernel Memory Management] Partner Allocator ② (Partner Allocator Allocating Memory Process)

, explains the basic partner allocator concept, and the memory allocation process;

The concept of partition buddy allocator: The Linux kernel adds support for "memory node" and "memory area" based on the basic partner allocator , which is "Partition Buddy Allocator" , the English name is "Zond Buddy Allocator";

The partition partner allocator focuses on a specific memory region of a specific memory node;

Features of "Partition Partner Allocator":

• The physical memory is grouped according to mobility to prevent memory fragmentation;
• Optimized "single page memory allocation" , reduced lock contention between CPUs, increased per ;

Second, the partition partner allocator source data structure

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1. free_area free area array

The members in the memory area zone structure are the array data structuresfree_area used to maintain free page blocks, and the subscript index of the array corresponds to the page block order;free_area

That free_area[0]is to say, it means $Level\; 0$ page block free memory, whichfree_area[2]means$Level\; 2$ page block free memory;

struct zone {
    
    
	...
	/* free areas of different sizes */
	struct free_area	free_area[MAX_ORDER];
	...
}

Source code path: linux-4.12\include\linux\mmzone.h #453

"memory area" struct zonestructure location:

Source code path: linux-4.12\include\linux\mmzone.h #350

Refer to [Linux Kernel Memory Management] Physical Memory Organization Structure ④ (Introduction to Memory Zone Zone | Zone Structure Source Code Analysis | Zone Structure Source Code) blog;

2. MAX_ORDER macro definition (the maximum order of pages in the free area)

struct free_area free_area[MAX_ORDER];The value of the MAX_ORDER macro is $11$ ,

MAX_ORDER is the largest order $11$ , the partner allocator can allocate a maximum of$2^{10}$ page blocks, or10${}^{10}$$10$ -order page block;

free_area[10]means $10$ -order page block free memory, which is$2^{10}$ page blocks${}^{;}$

#ifndef CONFIG_FORCE_MAX_ZONEORDERThe function is to determine whether a CONFIG_FORCE_MAX_ZONEORDERmacro definition is defined. The function of the macro definition is to "specify the maximum order". If not specified, the specified maximum order is $11$ ;

MAX_ORDER Macro definition source code:

/* Free memory management - zoned buddy allocator.  */
#ifndef CONFIG_FORCE_MAX_ZONEORDER
#define MAX_ORDER 11
#else
#define MAX_ORDER CONFIG_FORCE_MAX_ZONEORDER
#endif
#define MAX_ORDER_NR_PAGES (1 << (MAX_ORDER - 1))

Source path: linux-4.12\include\linux\mmzone.h #24