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

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Date:   Tue, 28 Sep 2021 12:39:19 +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 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.

I would not expect memblock_dbg once memblock might not actually be 
alive anymore.

-- 
Thanks,

David / dhildenb