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

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Date:   Tue, 28 Sep 2021 16:23:29 +0530
From:   Faiyaz Mohammed <faiyazm@...eaurora.org>
To:     David Hildenbrand <david@...hat.com>, 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 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.

> I would not expect memblock_dbg once memblock might not actually be
> alive anymore.
> 
Here we can add pr_info as well, but the intention is to get callsite
and address info when the memblock=debug is pass through command line
and it is for debugging purpose.

Thanks and regards,
Mohammed Faiyaz