linux-kernel - Re: [PATCH] arm64: use generic free_initrd

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Date:   Mon, 23 Sep 2019 15:41:46 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Mike Rapoport <rppt@...nel.org>, Laura Abbott <labbott@...hat.com>
Cc:     Mark Rutland <mark.rutland@....com>, linux-arch@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        linux-kernel@...r.kernel.org, Mike Rapoport <rppt@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: use generic free_initrd_mem()



On 09/16/2019 07:25 PM, Mike Rapoport wrote:
> (added linux-arch)
> 
> On Mon, Sep 16, 2019 at 08:23:29AM -0400, Laura Abbott wrote:
>> On 9/16/19 8:21 AM, Mike Rapoport wrote:
>>> From: Mike Rapoport <rppt@...ux.ibm.com>
>>>
>>> arm64 calls memblock_free() for the initrd area in its implementation of
>>> free_initrd_mem(), but this call has no actual effect that late in the boot
>>> process. By the time initrd is freed, all the reserved memory is managed by
>>> the page allocator and the memblock.reserved is unused, so there is no
>>> point to update it.
>>>
>>
>> People like to use memblock for keeping track of memory even if it has no
>> actual effect. We made this change explicitly (see 05c58752f9dc ("arm64: To remove
>> initrd reserved area entry from memblock") That said, moving to the generic
>> APIs would be nice. Maybe we can find another place to update the accounting?
> 
> Any other place in arch/arm64 would make it messy because it would have to
> duplicate keepinitrd logic.
> 
> We could put the memblock_free() in the generic free_initrd_mem() with
> something like:
> 
> diff --git a/init/initramfs.c b/init/initramfs.c
> index c47dad0..403c6a0 100644
> --- a/init/initramfs.c
> +++ b/init/initramfs.c
> @@ -531,6 +531,10 @@ void __weak free_initrd_mem(unsigned long start,
> unsigned long end)
>  {
>         free_reserved_area((void *)start, (void *)end, POISON_FREE_INITMEM,
>                         "initrd");
> +
> +#ifdef CONFIG_ARCH_KEEP_MEMBLOCK
> +       memblock_free(__virt_to_phys(start), end - start);
> +#endif
>  }

This makes sense.

>  
>  #ifdef CONFIG_KEXEC_CORE
> 
> 
> Then powerpc and s390 folks will also be able to track the initrd memory :)

Sure.

> 
>>> Without the memblock_free() call the only difference between arm64 and the
>>> generic versions of free_initrd_mem() is the memory poisoning. Switching
>>> arm64 to the generic version will enable the poisoning.
>>>
>>> Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
>>> ---
>>>
>>> I've boot tested it on qemu and I've checked that kexec works.
>>>
>>>  arch/arm64/mm/init.c | 8 --------
>>>  1 file changed, 8 deletions(-)
>>>
>>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>>> index f3c7952..8ad2934 100644
>>> --- a/arch/arm64/mm/init.c
>>> +++ b/arch/arm64/mm/init.c
>>> @@ -567,14 +567,6 @@ void free_initmem(void)
>>>  	unmap_kernel_range((u64)__init_begin, (u64)(__init_end - __init_begin));
>>>  }
>>> -#ifdef CONFIG_BLK_DEV_INITRD
>>> -void __init free_initrd_mem(unsigned long start, unsigned long end)
>>> -{
>>> -	free_reserved_area((void *)start, (void *)end, 0, "initrd");
>>> -	memblock_free(__virt_to_phys(start), end - start);
>>> -}
>>> -#endif
>>> -
>>>  /*
>>>   * Dump out memory limit information on panic.
>>>   */
>>>
>>
>