Subject: Re: [PATCH 06/15] powerpc: fadamp: simplify fadump_reserve_crash_area()

From: Hari Bathini <[email-masked]>
Date: Sat, 1 Aug 2020 16:23:15 +0530

On 01/08/20 3:48 pm, Mike Rapoport wrote:
> On Thu, Jul 30, 2020 at 10:15:13PM +1000, Michael Ellerman wrote:
>> Mike Rapoport <[email-masked]> writes:
>>> From: Mike Rapoport <[email-masked]>
>>>
>>> fadump_reserve_crash_area() reserves memory from a specified base address
>>> till the end of the RAM.
>>>
>>> Replace iteration through the memblock.memory with a single call to
>>> memblock_reserve() with appropriate  that will take care of proper memory
>>                                       ^
>>                                       parameters?
>>> reservation.
>>>
>>> Signed-off-by: Mike Rapoport <[email-masked]>
>>> ---
>>>   arch/powerpc/kernel/fadump.c | 20 +-------------------
>>>   1 file changed, 1 insertion(+), 19 deletions(-)
>>
>> I think this looks OK to me, but I don't have a setup to test it easily.
>> I've added Hari to Cc who might be able to.
>>
>> But I'll give you an ack in the hope that it works :)
> 
> Actually, I did some digging in the git log and the traversal was added
> there on purpose by the commit b71a693d3db3 ("powerpc/fadump: exclude
> memory holes while reserving memory in second kernel")

I was about to comment on the same :)
memblock_reserve() was being used until we ran into the issue talked 
about in the above commit...

> Presuming this is still reqruired I'm going to drop this patch and will

Yeah, it is still required..

> simply replace for_each_memblock() with for_each_mem_range() in v2.

Sounds right.

>   
>> Acked-by: Michael Ellerman <[email-masked]>
>>
>>
>>> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
>>> index 78ab9a6ee6ac..2446a61e3c25 100644
>>> --- a/arch/powerpc/kernel/fadump.c
>>> +++ b/arch/powerpc/kernel/fadump.c
>>> @@ -1658,25 +1658,7 @@ int __init fadump_reserve_mem(void)
>>>   /* Preserve everything above the base address */
>>>   static void __init fadump_reserve_crash_area(u64 base)
>>>   {
>>> -	struct memblock_region *reg;
>>> -	u64 mstart, msize;
>>> -
>>> -	for_each_memblock(memory, reg) {
>>> -		mstart = reg->base;
>>> -		msize  = reg->size;
>>> -
>>> -		if ((mstart + msize) < base)
>>> -			continue;
>>> -
>>> -		if (mstart < base) {
>>> -			msize -= (base - mstart);
>>> -			mstart = base;
>>> -		}
>>> -
>>> -		pr_info("Reserving %lluMB of memory at %#016llx for preserving crash data",
>>> -			(msize >> 20), mstart);
>>> -		memblock_reserve(mstart, msize);
>>> -	}
>>> +	memblock_reserve(base, memblock_end_of_DRAM() - base);
>>>   }
>>>   
>>>   unsigned long __init arch_reserved_kernel_pages(void)
>>> -- 
>>> 2.26.2
> 

Thanks
Hari