linux-kernel - [PATCH v2 1/3] memblock: free_unused_memmap: use pageblock units instead of MAX

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Message-Id: <20210519141436.11961-2-rppt@kernel.org>
Date:   Wed, 19 May 2021 17:14:34 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Mike Rapoport <rppt@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH v2 1/3] memblock: free_unused_memmap: use pageblock units instead of MAX_ORDER

From: Mike Rapoport <rppt@...ux.ibm.com>

The code that frees unused memory map uses rounds start and end of the
holes that are freed to MAX_ORDER_NR_PAGES to preserve continuity of the
memory map for MAX_ORDER regions.

Lots of core memory management functionality relies on homogeneity of the
memory map within each pageblock which size may differ from MAX_ORDER in
certain configurations.

Although currently, for the architectures that use free_unused_memmap(),
pageblock_order and MAX_ORDER are equivalent, it is cleaner to have common
notation thought mm code.

Replace MAX_ORDER_NR_PAGES with pageblock_nr_pages and update the comments
to make it more clear why the alignment to pageblock boundaries is
required.

Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
---
 mm/memblock.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index afaefa8fc6ab..97fa87541b5f 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1943,11 +1943,11 @@ static void __init free_unused_memmap(void)
 		start = min(start, ALIGN(prev_end, PAGES_PER_SECTION));
 #else
 		/*
-		 * Align down here since the VM subsystem insists that the
-		 * memmap entries are valid from the bank start aligned to
-		 * MAX_ORDER_NR_PAGES.
+		 * Align down here since many operations in VM subsystem
+		 * presume that there are no holes in the memory map inside
+		 * a pageblock
 		 */
-		start = round_down(start, MAX_ORDER_NR_PAGES);
+		start = round_down(start, pageblock_nr_pages);
 #endif
 
 		/*
@@ -1958,11 +1958,11 @@ static void __init free_unused_memmap(void)
 			free_memmap(prev_end, start);
 
 		/*
-		 * Align up here since the VM subsystem insists that the
-		 * memmap entries are valid from the bank end aligned to
-		 * MAX_ORDER_NR_PAGES.
+		 * Align up here since many operations in VM subsystem
+		 * presume that there are no holes in the memory map inside
+		 * a pageblock
 		 */
-		prev_end = ALIGN(end, MAX_ORDER_NR_PAGES);
+		prev_end = ALIGN(end, pageblock_nr_pages);
 	}
 
 #ifdef CONFIG_SPARSEMEM
-- 
2.28.0