linux-kernel - [PATCH 4/6] x86, mm: make split_mem

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Date:   Tue, 12 Feb 2019 10:12:13 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.or,
        tglx@...utronix.de, Wei Yang <richardw.yang@...ux.intel.com>
Subject: [PATCH 4/6] x86, mm: make split_mem_range() more easy to read

As the comment explains, there are at most 5 possible ranges:

              kkkmmmGGGmmmkkk
              (A)(B)(C)(D)(E)

While there are two ways to perceive:

    * C & D are extra ranges on X86_64
    * B & C are extra ranges on X86_64

Current implementation takes the first way, which leads to handling
end_pfn of B differently:

    * align to PMD on X86_32
    * align to PUD on X86_64

If we take the second way, we don't need to handle it differently.

    * the end_pfn of B only need to align to PUD
    * the end_pfn of D only need to align to PMD

This patch changes the implementation from the first perception to the
second to reduce one different handling on end_pfn. After doing so, the
code is easier to read.

Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
---
 arch/x86/mm/init.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 2b782dcd6d71..87275238dbb0 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -389,25 +389,21 @@ static int __meminit split_mem_range(struct map_range *mr,
 		pfn = end_pfn;
 	}
 
+#ifdef CONFIG_X86_64
 	/*
 	 * 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));
-#else /* CONFIG_X86_64 */
 	end_pfn = round_up(pfn, PFN_DOWN(PUD_SIZE));
 	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));
 		pfn = end_pfn;
 	}
 
-#ifdef CONFIG_X86_64
 	/*
 	 * Range (C):
 	 * big page (1G) range
@@ -420,6 +416,7 @@ static int __meminit split_mem_range(struct map_range *mr,
 				 ((1<<PG_LEVEL_2M)|(1<<PG_LEVEL_1G)));
 		pfn = end_pfn;
 	}
+#endif
 
 	/*
 	 * Range (D):
@@ -432,7 +429,6 @@ static int __meminit split_mem_range(struct map_range *mr,
 				page_size_mask & (1<<PG_LEVEL_2M));
 		pfn = end_pfn;
 	}
-#endif
 
 	/*
 	 * Range (E):
-- 
2.19.1