linux-kernel - Re: [PATCH v2 2/3] mm, page_owner: decouple freeing stack trace from debug

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Date:   Mon, 30 Sep 2019 23:39:34 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Qian Cai <cai@....pw>, Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Walter Wu <walter-zh.wu@...iatek.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>
Subject: Re: [PATCH v2 2/3] mm, page_owner: decouple freeing stack trace from
 debug_pagealloc

On 9/30/19 2:49 PM, Qian Cai wrote:
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -3237,6 +3237,14 @@
>>  			we can turn it on.
>>  			on: enable the feature
>>  
>> +	page_owner_free=
>> +			[KNL] When enabled together with page_owner, store also
>> +			the stack of who frees a page, for error page dump
>> +			purposes. This is also implicitly enabled by
>> +			debug_pagealloc=on or KASAN, so only page_owner=on is
>> +			sufficient in those cases.
>> +			on: enable the feature
>> +
> 
> If users are willing to set page_owner=on, what prevent them from enabling KASAN
> as well? That way, we don't need this additional parameter.

Well, my use case is shipping production kernels with CONFIG_PAGE_OWNER
and CONFIG_DEBUG_PAGEALLOC enabled, and instructing users to boot-time
enable only for troubleshooting a crash or memory leak, without a need
to install a debug kernel. Things like static keys and page_ext
allocations makes this possible without CPU and memory overhead when not
boot-time enabled. I don't know too much about KASAN internals, but I
assume it's not possible to use it that way on production kernels yet?

> I read that KASAN
> supposes to be semi-production use ready, so the overhead is relatively low.
> There is even a choice to have KASAN_SW_TAGS on arm64 to work better with small
> devices.