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Subject: Re: [PATCH 2/2] mm, page_owner: Skip unnecessary stack_trace entries
To: Prakash Gupta <guptap@codeaurora.org>, akpm@linux-foundation.org,
        mhocko@suse.com, will.deacon@arm.com, catalin.marinas@arm.com,
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References: <1504078343-28754-1-git-send-email-guptap@codeaurora.org>
 <1504078343-28754-2-git-send-email-guptap@codeaurora.org>
From: Vlastimil Babka <vbabka@suse.cz>
Message-ID: <82346e0c-176a-dc11-c535-47d023f237a8@suse.cz>
Date: Thu, 31 Aug 2017 09:34:38 +0200
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On 08/30/2017 09:32 AM, Prakash Gupta wrote:
> The page_owner stacktrace always begin as follows:
> 
> [<ffffff987bfd48f4>] save_stack+0x40/0xc8
> [<ffffff987bfd4da8>] __set_page_owner+0x3c/0x6c

Hmm, on x86_64 it looks like this:

 save_stack_trace+0x16/0x20
 save_stack+0x43/0xe0
 __set_page_owner+0x24/0x50

So after your patch there's still __set_page_owner. Seems x86 needs
something similar to your arm64 patch 1/2?

> These two entries do not provide any useful information and limits the
> available stacktrace depth.  The page_owner stacktrace was skipping caller
> function from stack entries but this was missed with commit f2ca0b557107
> ("mm/page_owner: use stackdepot to store stacktrace")
> 
> Example page_owner entry after the patch:
> 
> Page allocated via order 0, mask 0x8(ffffff80085fb714)
> PFN 654411 type Movable Block 639 type CMA Flags 0x0(ffffffbe5c7f12c0)
> [<ffffff9b64989c14>] post_alloc_hook+0x70/0x80
> ...
> [<ffffff9b651216e8>] msm_comm_try_state+0x5f8/0x14f4
> [<ffffff9b6512486c>] msm_vidc_open+0x5e4/0x7d0
> [<ffffff9b65113674>] msm_v4l2_open+0xa8/0x224
> 
> Fixes: f2ca0b557107 ("mm/page_owner: use stackdepot to store stacktrace")
> Signed-off-by: Prakash Gupta <guptap@codeaurora.org>

The patch itself improves the output regardless of whether we fix the
x86 internals, so:

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  mm/page_owner.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 10d16fc45bd9..75b7c39bf1df 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -139,7 +139,7 @@ static noinline depot_stack_handle_t save_stack(gfp_t flags)
>  		.nr_entries = 0,
>  		.entries = entries,
>  		.max_entries = PAGE_OWNER_STACK_DEPTH,
> -		.skip = 0
> +		.skip = 2
>  	};
>  	depot_stack_handle_t handle;
>  
>