Linux内存从0到1学习笔记(8.5，CMA内存分配)

Posted 2022-04-29 高桐@BILL

CMA是通过cma_alloc分配的。cma_alloc() --> alloc_contig_range(..., MIGRATE_CMA,...)，向刚才释放给buddy system的MIGRATE_CMA类型页面，重新“收集”过来。

linux_mainline-5.17.0/mm/cma.c

416  /**
417   * cma_alloc() - allocate pages from contiguous area
418   * @cma:   Contiguous memory region for which the allocation is performed.
419   * @count: Requested number of pages.
420   * @align: Requested alignment of pages (in PAGE_SIZE order).
421   * @no_warn: Avoid printing message about failed allocation
422   *
423   * This function allocates part of contiguous memory on specific
424   * contiguous memory area.
425   */
426  struct page *cma_alloc(struct cma *cma, unsigned long count,
427  		       unsigned int align, bool no_warn)
428  
429  	unsigned long mask, offset;
430  	unsigned long pfn = -1;
431  	unsigned long start = 0;
432  	unsigned long bitmap_maxno, bitmap_no, bitmap_count;
433  	unsigned long i;
434  	struct page *page = N