linux-kernel - Re: [PATCH v1] mm: page_alloc: Add debug log in free_reserved

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Date:   Wed, 29 Sep 2021 19:03:50 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Faiyaz Mohammed <faiyazm@...eaurora.org>,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     guptap@...eaurora.org
Subject: Re: [PATCH v1] mm: page_alloc: Add debug log in free_reserved_area
 for static memory

On 29.09.21 10:58, Faiyaz Mohammed wrote:
> 
> 
> On 9/28/2021 4:46 PM, David Hildenbrand wrote:
>> On 28.09.21 12:53, Faiyaz Mohammed wrote:
>>>
>>>
>>> On 9/28/2021 4:09 PM, David Hildenbrand wrote:
>>>> On 28.09.21 11:04, Faiyaz Mohammed wrote:
>>>>> For INITRD and initmem memory is reserved through "memblock_reserve"
>>>>> during boot up but it is free via "free_reserved_area" instead
>>>>> of "memblock_free".
>>>>> For example:
>>>>> [    0.294848] Freeing initrd memory: 12K.
>>>>> [    0.696688] Freeing unused kernel memory: 4096K.
>>>>>
>>>>> To get the start and end address of the above freed memory and to
>>>>> account
>>>>> proper memblock added memblock_dbg log in "free_reserved_area".
>>>>> After adding log:
>>>>> [    0.294837] memblock_free: [0x00000083600000-0x00000083603000]
>>>>> free_initrd_mem+0x20/0x28
>>>>> [    0.294848] Freeing initrd memory: 12K.
>>>>> [    0.695246] memblock_free: [0x00000081600000-0x00000081a00000]
>>>>> free_initmem+0x70/0xc8
>>>>> [    0.696688] Freeing unused kernel memory: 4096K.
>>>>>
>>>>> Signed-off-by: Faiyaz Mohammed <faiyazm@...eaurora.org>
>>>>> ---
>>>>>     mm/page_alloc.c | 5 +++++
>>>>>     1 file changed, 5 insertions(+)
>>>>>
>>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>>>> index b37435c..f85c3b2 100644
>>>>> --- a/mm/page_alloc.c
>>>>> +++ b/mm/page_alloc.c
>>>>> @@ -8129,6 +8129,11 @@ unsigned long free_reserved_area(void *start,
>>>>> void *end, int poison, const char
>>>>>             pr_info("Freeing %s memory: %ldK\n",
>>>>>                 s, pages << (PAGE_SHIFT - 10));
>>>>>     +#ifdef CONFIG_HAVE_MEMBLOCK
>>>>> +        memblock_dbg("memblock_free: [%#016llx-%#016llx] %pS\n",
>>>>> +            __pa(start), __pa(end), (void *)_RET_IP_);
>>>>> +#endif
>>>>
>>>> IMHO, the "memblock_free" part is misleading. Something was allocated
>>>> early via memblock, then we transitioned to the buddy, now we're freeing
>>>> that early allocation via the buddy.
>>>> Yes, we're freeing the early allocation via buddy, but for proper
>>> memblock accounting we need this debug print.
>>>
>>
>> What do you mean with "accounting" ? These are debug statements.
>>
>>
> Yes, these are debug statements, which help to know the a-b address
> belongs to x callsite. This info is required when memblock=debug is
> passed through command line and CONFIG_HAVE_MEMBLOCK is enabled.

The issue I'm having is talking in the name of memblock "memblock_dbg, 
memblock_free", when memblock might no longer be around. We have other 
places where we free early memblock allocations back to the buddy.

-- 
Thanks,

David / dhildenb