Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [Patch v2 3/4] mm/page_alloc.c: pass all bad reasons to
 bad_page()
To:     Michal Hocko <mhocko@kernel.org>,
        Wei Yang <richardw.yang@linux.intel.com>
Cc:     akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, rientjes@google.com
References: <20200120030415.15925-1-richardw.yang@linux.intel.com>
 <20200120030415.15925-4-richardw.yang@linux.intel.com>
 <20200120102200.GW18451@dhcp22.suse.cz>
From:   Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <2288c80c-42f7-a161-58cf-47cf07699202@arm.com>
Date:   Tue, 21 Jan 2020 11:38:29 +0530
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.9.1
MIME-Version: 1.0
In-Reply-To: <20200120102200.GW18451@dhcp22.suse.cz>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


On 01/20/2020 03:52 PM, Michal Hocko wrote:
> On Mon 20-01-20 11:04:14, Wei Yang wrote:
>> Now we can pass all bad reasons to __dump_page().
> And we do we want to do that? The dump of the page will tell us the
> whole story so a single and the most important reason sounds like a
> better implementation. The code is also more subtle because each caller
> of the function has to be aware of how many reasons there might be.
> Not to mention that you need a room for 5 pointers on the stack and this
> and page allocator might be called from deeper call chains.
> 

Two paths which lead to __dump_page(), dump_page() and bad_page().
Callers of dump_page() can give a single reason what they consider the
most important which leads to page dumping. This makes sense but gets
trickier in bad_page() path. At present, free_pages_check_bad() and
check_new_page_bad() has a sequence of 'if' statements which decides
"most important" reason for __dump_page() without much rationale and
similar in case of free_tail_pages_check() as well. As all information
about the page for corresponding reasons are printed with __dump_page()
anyways, do free_pages_check_bad() or check_new_page_bad() really need
to provide any particular single reason ?