p; */
r->start = base;
r->size = size;
r->dev = dev;
cma_reserved_count++;
pr_info("CMA: reserved %ld MiB at %08lx\n", size / SZ_1M,
(unsigned long)base);
/* Architecture specific contiguous memory fixup. */
dma_contiguous_early_fixup(base, size);
return 0;
err:
pr_err("CMA: failed to reserve %ld MiB\n", size / SZ_1M);
return base;
}
由此可见，连续内存区域也是在内核启动的早期，通过__memblock_alloc_base()拿到的。
另外：
drivers/base/dma-contiguous.c里面的core_initcall()会导致cma_init_reserved_areas()被调用：
cma_create_area()会调用cma_activate_area(),cma_activate_area()函数则会针对每个page调用：
init_cma_reserved_pageblock(pfn_to_page(base_pfn));
这个函数则会通过set_pageblock_migratetype(page, MIGRATE_CMA)将页设置为MIGRATE_CMA类型的：
#ifdef CONFIG_CMA
/* Free whole pageblock and set it's migration type to MIGRATE_CMA. */
void __init init_cma_reserved_pageblock(struct page *page)
{
unsigned i = pageblock_nr_pages;
struct page *p = page;
do {
__ClearPageReserved(p);
set_page_count(p, 0);
} while (++p, --i);
set_page_refcounted(page);
set_pageblock_migratetype(page, MIGRATE_CMA);
__free_pages(page, pageblock_order);
totalram_pages += pageblock_nr_pages;
}
#endif
同时其中调用的__free_pages(page, pageblock_order);最终会调用到__free_one_page(page, zone, order, migratetype);
相关的page会被加到MIGRATE_CMA的free_list上面去：
list_add(&page->lru, &zone->free_area[order].free_list[migratetype]);
2. 申请连续内存
申请连续内存仍然使用标准的arch/arm/mm/dma-mapping.c中定义的dma_alloc_coherent()和dma_alloc_writecombine()，这二者会间接调用drivers/base/dma-contiguous.c中的
struct page *dma_alloc_from_contiguous(struct device *dev, int count,
unsigned int align)
->
struct page *dma_alloc_from_contiguous(struct device *dev, int count,
unsigned int align)
{
...
for (;;) {
pageno = bitmap_find_next_zero_area(cma->bitmap, cma->count,
start, count, mask);
if (pageno >= cma->count) {
ret = -ENOMEM;
goto error;
}
pfn = cma->base_pfn + pageno;
ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA);
if (ret == 0) {
bitmap_set(cma->bitmap, pageno, count);
break;
} else if (ret != -EBUSY) {
goto error;
}
pr_debug("%s(): memory range at %p is busy, retrying\n",
__func__, pfn_to_page(pfn));
/* try again with a bit different memory target */
start = pageno + mask + 1;
}
...
}
--》
int alloc_contig_range(unsigned long start, unsigned long end,
unsigned migratetype)
需要隔离page，隔离page的作用通过代码的注释可以体现：
/*
* What we do here is we mark all pageblocks in range as
* MIGRATE_ISOLATE. Because of the way page allocator work, we
* align the range to MAX_ORDER pages so that page allocator
* won't try to merge buddies from different pageblocks and
* change MIGRATE_ISOLATE to some other migration type.
*
* Once the pageblocks