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Subject: Re: [PATCH v1] mm: page_alloc: Add debug log in free_reserved_area
 for static memory
To:     David Hildenbrand <david@redhat.com>, akpm@linux-foundation.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc:     guptap@codeaurora.org
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From:   Faiyaz Mohammed <faiyazm@codeaurora.org>
Message-ID: <88df48af-901b-5765-d92c-6d14c2b1f73e@codeaurora.org>
Date:   Wed, 6 Oct 2021 17:43:08 +0530
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Hi,

Sorry for delayed response.

On 9/29/2021 10:33 PM, David Hildenbrand wrote:
> 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@codeaurora.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.
I didn't find place where we free early memblock allocation back to the
buddy.

Why "memblock_dbg" print with "memblock_free" string?.
- After buddy took over, buddy will free memblock reserved memory
through free_reserved_area and it will print the freed memory size, but
the freed memory through buddy still be part of memblock.reserved.regions.
- To know the address ranges, added the "memblock_dbg" print along with
"membloc_free" string.
- If it is misleading or confusing, we can remove the "memblock_free"
string from the "memblock_dgb" print and we can just print the address
range when "memlock=debug" pass through command line.

Thanks and regards,
Mohammed Faiyaz