linux-kernel - [PATCH] RISC-V: Consider sparse memory while removing unusable memory

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Date:   Fri, 11 Sep 2020 17:23:41 -0700
From:   Atish Patra <atish.patra@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Atish Patra <atish.patra@....com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup.patel@....com>,
        linux-riscv@...ts.infradead.org,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Zong Li <zong.li@...ive.com>, Mike Rapoport <rppt@...nel.org>
Subject: [PATCH] RISC-V: Consider sparse memory while removing unusable memory

Currently, any usable memory area beyond page_offset is removed by adding the
memory sizes from each memblock. That may not work for sparse memory
as memory regions can be very far apart resulting incorrect removal of some
usable memory.

Just use the start of the first memory block and the end of the last memory
block to compute the size of the total memory that can be used.

Signed-off-by: Atish Patra <atish.patra@....com>
---
 arch/riscv/mm/init.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 787c75f751a5..188281fc2816 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -147,7 +147,6 @@ void __init setup_bootmem(void)
 {
 	struct memblock_region *reg;
 	phys_addr_t mem_size = 0;
-	phys_addr_t total_mem = 0;
 	phys_addr_t mem_start, end = 0;
 	phys_addr_t vmlinux_end = __pa_symbol(&_end);
 	phys_addr_t vmlinux_start = __pa_symbol(&_start);
@@ -155,18 +154,17 @@ void __init setup_bootmem(void)
 	/* Find the memory region containing the kernel */
 	for_each_memblock(memory, reg) {
 		end = reg->base + reg->size;
-		if (!total_mem)
+		if (!mem_start)
 			mem_start = reg->base;
 		if (reg->base <= vmlinux_start && vmlinux_end <= end)
 			BUG_ON(reg->size == 0);
-		total_mem = total_mem + reg->size;
 	}
 
 	/*
 	 * Remove memblock from the end of usable area to the
 	 * end of region
 	 */
-	mem_size = min(total_mem, (phys_addr_t)-PAGE_OFFSET);
+	mem_size = min(end - mem_start, (phys_addr_t)-PAGE_OFFSET);
 	if (mem_start + mem_size < end)
 		memblock_remove(mem_start + mem_size,
 				end - mem_start - mem_size);
-- 
2.24.0