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SubjectRe: [PATCH] RISC-V: Consider sparse memory while removing unusable memory
Hello Atish,

On Fri, Sep 11, 2020 at 05:23:41PM -0700, Atish Patra wrote:
> 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.

If I understand correctly, the memory with physical addresses larger
than (-PAGE_OFFSET) cannot be used. Since it was aready
memblock_add()'ed during device tree parsing, you need to remove it from
memblock.

For that you can use memblock_enforce_memory_limit(-PAGE_OFFSET).

> 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@wdc.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
>

--
Sincerely yours,
Mike.

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