linux-kernel - Re: [PATCH 2/2] mm, page_owner: Skip unnecessary stack

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Date:   Fri, 1 Sep 2017 10:30:23 +0530
From:   Prakash Gupta <guptap@...eaurora.org>
To:     Vlastimil Babka <vbabka@...e.cz>, akpm@...ux-foundation.org,
        mhocko@...e.com, will.deacon@....com, catalin.marinas@....com,
        iamjoonsoo.kim@....com, rmk+kernel@....linux.org.uk,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 2/2] mm, page_owner: Skip unnecessary stack_trace entries


On 8/31/2017 1:04 PM, Vlastimil Babka wrote:
> 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?

Yes, that's correct.

> 
>> 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@...eaurora.org>
> 
> The patch itself improves the output regardless of whether we fix the
> x86 internals, so:
> 
> Acked-by: Vlastimil Babka <vbabka@...e.cz>

Thanks.

> 
>> ---
>>   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;
>>   
>>
>