Describing the possible ranges in split and marking ranges with name to help audience understand the logic.
Also this prepares to illustrate a code refine next. Signed-off-by: Wei Yang <[email protected]> --- arch/x86/mm/init.c | 51 ++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 45 insertions(+), 6 deletions(-) diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c index 6fb84be79c7c..2b782dcd6d71 100644 --- a/arch/x86/mm/init.c +++ b/arch/x86/mm/init.c @@ -328,6 +328,31 @@ static const char *page_size_string(struct map_range *mr) return str_4k; } +/* + * There are 3 types of ranges: + * + * k : 4K size + * m : 2M size + * G : 1G size + * + * 1G size is only valid when CONFIG_X86_64 is set. + * + * So we can describe the possible ranges like below: + * + * kkkmmmGGGmmmkkk + * (A)(B)(C)(D)(E) + * + * This means there are at most: + * + * 3 ranges when CONFIG_X86_32 is set + * 5 ranges when CONFIG_X86_64 is set + * + * which corresponds to the definition of NR_RANGE_MR. + * + * split_mem_range() does the split from low to high. By naming these ranges + * to A, B, C, D, E respectively and marking the name in following comment, it + * may help you to understand how ranges are split. + */ static int __meminit split_mem_range(struct map_range *mr, unsigned long start, unsigned long end) @@ -338,7 +363,10 @@ static int __meminit split_mem_range(struct map_range *mr, limit_pfn = PFN_DOWN(end); - /* head if not big page alignment ? */ + /* + * Range (A): + * head if not big page alignment ? + */ pfn = start_pfn = PFN_DOWN(start); #ifdef CONFIG_X86_32 /* @@ -361,7 +389,10 @@ static int __meminit split_mem_range(struct map_range *mr, pfn = end_pfn; } - /* big page (2M) range */ + /* + * Range (B): + * big page (2M) range + */ start_pfn = round_up(pfn, PFN_DOWN(PMD_SIZE)); #ifdef CONFIG_X86_32 end_pfn = round_down(limit_pfn, PFN_DOWN(PMD_SIZE)); @@ -370,7 +401,6 @@ static int __meminit split_mem_range(struct map_range *mr, if (end_pfn > round_down(limit_pfn, PFN_DOWN(PMD_SIZE))) end_pfn = round_down(limit_pfn, PFN_DOWN(PMD_SIZE)); #endif - if (start_pfn < end_pfn) { nr_range = save_mr(mr, nr_range, start_pfn, end_pfn, page_size_mask & (1<<PG_LEVEL_2M)); @@ -378,7 +408,10 @@ static int __meminit split_mem_range(struct map_range *mr, } #ifdef CONFIG_X86_64 - /* big page (1G) range */ + /* + * Range (C): + * big page (1G) range + */ start_pfn = round_up(pfn, PFN_DOWN(PUD_SIZE)); end_pfn = round_down(limit_pfn, PFN_DOWN(PUD_SIZE)); if (start_pfn < end_pfn) { @@ -388,7 +421,10 @@ static int __meminit split_mem_range(struct map_range *mr, pfn = end_pfn; } - /* tail is not big page (1G) alignment */ + /* + * Range (D): + * big page (2M) range + */ start_pfn = round_up(pfn, PFN_DOWN(PMD_SIZE)); end_pfn = round_down(limit_pfn, PFN_DOWN(PMD_SIZE)); if (start_pfn < end_pfn) { @@ -398,7 +434,10 @@ static int __meminit split_mem_range(struct map_range *mr, } #endif - /* tail is not big page (2M) alignment */ + /* + * Range (E): + * tail is not big page (2M) alignment + */ start_pfn = pfn; end_pfn = limit_pfn; nr_range = save_mr(mr, nr_range, start_pfn, end_pfn, 0); -- 2.19.1
