(cc's added)
On Thu, 23 Oct 2014 17:56:53 +0100 Zubair Lutfullah Kakakhel
<[email protected]> wrote:
> The default region counts are set to 1 with a comment saying empty
> dummy entry.
>
> If this is a dummy entry, should this be changed to 0?
>
> We have faced this in mips/kernel/setup.c arch_mem_init.
>
> cma uses memblock. But even with cma disabled.
> The for_each_memblock(reserved, reg) goes inside the loop.
> Even without any reserved regions.
>
> Traced it to the following, when the macro
> for_each_memblock(memblock_type, region) is used.
>
> It expands to add the cnt variable.
>
> for (region = memblock.memblock_type.regions; \
> region < (memblock.memblock_type.regions + memblock.memblock_type.cnt);
> \
> region++)
>
> In the corner case, that there are no reserved regions.
> Due to the default 1 value of cnt.
> The loop under for_each_memblock still runs once.
>
> Even when there is no reserved region.
>
> Is this by design? or unintentional?
> It might be that this loop runs an extra time every instance out there?
> ---
> mm/memblock.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 6d2f219..b91301c 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -33,16 +33,16 @@ static struct memblock_region
> memblock_physmem_init_regions[INIT_PHYSMEM_REGIONS
>
> struct memblock memblock __initdata_memblock = {
> .memory.regions = memblock_memory_init_regions,
> - .memory.cnt = 1, /* empty dummy entry */
> + .memory.cnt = 0, /* empty dummy entry */
> .memory.max = INIT_MEMBLOCK_REGIONS,
>
> .reserved.regions = memblock_reserved_init_regions,
> - .reserved.cnt = 1, /* empty dummy entry */
> + .reserved.cnt = 0, /* empty dummy entry */
> .reserved.max = INIT_MEMBLOCK_REGIONS,
>
> #ifdef CONFIG_HAVE_MEMBLOCK_PHYS_MAP
> .physmem.regions = memblock_physmem_init_regions,
> - .physmem.cnt = 1, /* empty dummy entry */
> + .physmem.cnt = 0, /* empty dummy entry */
> .physmem.max = INIT_PHYSMEM_REGIONS,
> #endif
>
> --
> 1.9.1
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