linux-kernel - [PATCH 5.10 1/5] memblock: free_unused_memmap: use pageblock units instead of MAX

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Date:   Mon, 13 Dec 2021 17:41:31 +0800
From:   Mark-PK Tsai <mark-pk.tsai@...iatek.com>
To:     <stable@...r.kernel.org>
CC:     <rppt@...nel.org>, <akpm@...ux-foundation.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux@...linux.org.uk>, <rppt@...ux.ibm.com>, <tony@...mide.com>,
        <wangkefeng.wang@...wei.com>, <mark-pk.tsai@...iatek.com>,
        <yj.chiang@...iatek.com>
Subject: [PATCH 5.10 1/5] memblock: free_unused_memmap: use pageblock units instead of MAX_ORDER

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

[ Upstream commit e2a86800d58639b3acde7eaeb9eb393dca066e08 ]

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>
Tested-by: Tony Lindgren <tony@...mide.com>
Link: https://lore.kernel.org/lkml/20210630071211.21011-1-rppt@kernel.org/
[backport upstream modification in mm/memblock.c to arch/arm/mm/init.c]
Signed-off-by: Mark-PK Tsai <mark-pk.tsai@...iatek.com>
---
 arch/arm/mm/init.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 75f3ab531bdf..8440b6027598 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -315,11 +315,11 @@ static void __init free_unused_memmap(void)
 				 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
 		/*
 		 * If we had a previous bank, and there is a space
@@ -329,11 +329,11 @@ 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
-- 
2.18.0