arm, arm64: move free_unused_memmap() to generic mm

ARM and ARM64 free unused parts of the memory map just before the
initialization of the page allocator. To allow holes in the memory map both
architectures overload pfn_valid() and define HAVE_ARCH_PFN_VALID.

Allowing holes in the memory map for FLATMEM may be useful for small
machines, such as ARC and m68k and will enable those architectures to cease
using DISCONTIGMEM and still support more than one memory bank.

Move the functions that free unused memory map to generic mm and enable
them in case HAVE_ARCH_PFN_VALID=y.

Link: https://lkml.kernel.org/r/20201101170454.9567-10-rppt@kernel.org
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>	[arm64]
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Greg Ungerer <gerg@linux-m68k.org>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Meelis Roos <mroos@linux.ee>
Cc: Michael Schmitz <schmitzmic@gmail.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 80 insertions, 0 deletions

diff --git a/mm/memblock.c b/mm/memblock.c
index b68ee86788af..049df4163a97 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1926,6 +1926,85 @@ static int __init early_memblock(char *p)
 }
 early_param("memblock", early_memblock);
 
+static void __init free_memmap(unsigned long start_pfn, unsigned long end_pfn)
+{
+	struct page *start_pg, *end_pg;
+	phys_addr_t pg, pgend;
+
+	/*
+	 * Convert start_pfn/end_pfn to a struct page pointer.
+	 */
+	start_pg = pfn_to_page(start_pfn - 1) + 1;
+	end_pg = pfn_to_page(end_pfn - 1) + 1;
+
+	/*
+	 * Convert to physical addresses, and round start upwards and end
+	 * downwards.
+	 */
+	pg = PAGE_ALIGN(__pa(start_pg));
+	pgend = __pa(end_pg) & PAGE_MASK;
+
+	/*
+	 * If there are free pages between these, free the section of the
+	 * memmap array.
+	 */
+	if (pg < pgend)
+		memblock_free(pg, pgend - pg);
+}
+
+/*
+ * The mem_map array can get very big.  Free the unused area of the memory map.
+ */
+static void __init free_unused_memmap(void)
+{
+	unsigned long start, end, prev_end = 0;
+	int i;
+
+	if (!IS_ENABLED(CONFIG_HAVE_ARCH_PFN_VALID) ||
+	    IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP))
+		return;
+
+	/*
+	 * This relies on each bank being in address order.
+	 * The banks are sorted previously in bootmem_init().
+	 */
+	for_each_mem_pfn_range(i, MAX_NUMNODES, &start, &end, NULL) {
+#ifdef CONFIG_SPARSEMEM
+		/*
+		 * Take care not to free memmap entries that don't exist
+		 * due to SPARSEMEM sections which aren't present.
+		 */
+		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.
+		 */
+		start = round_down(start, MAX_ORDER_NR_PAGES);
+#endif
+
+		/*
+		 * If we had a previous bank, and there is a space
+		 * between the current bank and the previous, free it.
+		 */
+		if (prev_end && prev_end < start)
+			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.
+		 */
+		prev_end = ALIGN(end, MAX_ORDER_NR_PAGES);
+	}
+
+#ifdef CONFIG_SPARSEMEM
+	if (!IS_ALIGNED(prev_end, PAGES_PER_SECTION))
+		free_memmap(prev_end, ALIGN(prev_end, PAGES_PER_SECTION));
+#endif
+}
+
 static void __init __free_pages_memory(unsigned long start, unsigned long end)
 {
 	int order;
@@ -2012,6 +2091,7 @@ unsigned long __init memblock_free_all(void)
 {
 	unsigned long pages;
 
+	free_unused_memmap();
 	reset_all_zones_managed_pages();
 
 	pages = free_low_memory_core_early();