linux 内存管理之五bootmem 分配器 2.4.22

news2025/11/1 7:30:57

内核的bootmem 分配器又叫自举内存分配器，其内涵即自己初始化自己的一个内存分配器
其初始化过程已在上篇[ARM 架构物理内存初始化]，(https://blog.csdn.net/zsj1126/article/details/116430903)介绍

本文主要关注该分配器提供的主要接口和用途
在这里插入图片描述


static void * __init __alloc_bootmem_core (bootmem_data_t *bdata, 
	unsigned long size, unsigned long align, unsigned long goal)

bdata, 指向node的bootmem分配器j结构
size ：申请空间字节数
align: 申请地址对齐大小
goal: 目标起始位置

	offset = 0;
	if (align &&
	    (bdata->node_boot_start & (align - 1UL)) != 0)
		offset = (align - (bdata->node_boot_start & (align - 1UL)));
	offset >>= PAGE_SHIFT;

	/*
	 * We try to allocate bootmem pages above 'goal'
	 * first, then we try to allocate lower pages.
	 */
	if (goal && (goal >= bdata->node_boot_start) && 
			((goal >> PAGE_SHIFT) < bdata->node_low_pfn)) {
		preferred = goal - bdata->node_boot_start;
	} else
		preferred = 0;

	preferred = ((preferred + align - 1) & ~(align - 1)) >> PAGE_SHIFT;
	preferred += offset;
	areasize = (size+PAGE_SIZE-1)/PAGE_SIZE;
	incr = align >> PAGE_SHIFT ? : 1; // 步进对齐

以页为单位分配，起始地址对齐和计算，如goal 非0 ，则从goal 开始扫描。

restart_scan:
	for (i = preferred; i < eidx; i += incr) {
		unsigned long j;
		if (test_bit(i, bdata->node_bootmem_map))
			continue;
		for (j = i + 1; j < i + areasize; ++j) {
			if (j >= eidx)
				goto fail_block;
			if (test_bit (j, bdata->node_bootmem_map))
				goto fail_block;
		}
		start = i;
		goto found;
	fail_block:;
	}
	if (preferred) {
		preferred = offset;
		goto restart_scan;
	}
	return NULL;