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 v3] mm/page_owner: fix for deferred struct page init
To:     Michal Hocko <mhocko@kernel.org>
Cc:     akpm@linux-foundation.org, Pavel.Tatashin@microsoft.com,
        mingo@kernel.org, mgorman@techsingularity.net,
        iamjoonsoo.kim@lge.com, tglx@linutronix.de, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <20190103115114.GL31793@dhcp22.suse.cz>
 <e3ff1455-06cc-063e-24f0-3b525c345b84@lca.pw>
 <20190103165927.GU31793@dhcp22.suse.cz>
 <5d8f3a98-a954-c8ab-83d9-2f94c614f268@lca.pw>
 <20190103190715.GZ31793@dhcp22.suse.cz>
 <62e96e34-7ea9-491a-b5b6-4828da980d48@lca.pw>
 <20190103202235.GE31793@dhcp22.suse.cz>
 <a5666d82-b7ad-4b90-5f4e-fd22afc3e1dc@lca.pw>
 <20190104130906.GO31793@dhcp22.suse.cz>
 <e4ad9d12-387d-1cc6-f404-cae6d43ccf80@lca.pw>
 <20190104151737.GT31793@dhcp22.suse.cz>
From:   Qian Cai <cai@lca.pw>
Message-ID: <c8faf7eb-d23f-4ef7-3432-0acc7165f883@lca.pw>
Date:   Fri, 4 Jan 2019 10:25:12 -0500
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0)
 Gecko/20100101 Thunderbird/60.3.3
MIME-Version: 1.0
In-Reply-To: <20190104151737.GT31793@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 1/4/19 10:17 AM, Michal Hocko wrote:
> On Fri 04-01-19 10:01:40, Qian Cai wrote:
>> On 1/4/19 8:09 AM, Michal Hocko wrote:
>>>> Here is the number without DEFERRED_STRUCT_PAGE_INIT.
>>>>
>>>> == page_ext_init() after page_alloc_init_late() ==
>>>> Node 0, zone DMA: page owner found early allocated 0 pages
>>>> Node 0, zone DMA32: page owner found early allocated 7009 pages
>>>> Node 0, zone Normal: page owner found early allocated 85827 pages
>>>> Node 4, zone Normal: page owner found early allocated 75063 pages
>>>>
>>>> == page_ext_init() before kmemleak_init() ==
>>>> Node 0, zone DMA: page owner found early allocated 0 pages
>>>> Node 0, zone DMA32: page owner found early allocated 6654 pages
>>>> Node 0, zone Normal: page owner found early allocated 41907 pages
>>>> Node 4, zone Normal: page owner found early allocated 41356 pages
>>>>
>>>> So, it told us that it will miss tens of thousands of early page allocation call
>>>> sites.
>>>
>>> This is an answer for the first part of the question (how much). The
>>> second is _do_we_care_?
>>
>> Well, the purpose of this simple "ugly" ifdef is to avoid a regression for the
>> existing page_owner users with DEFERRED_STRUCT_PAGE_INIT deselected that would
>> start to miss tens of thousands early page allocation call sites.
> 
> I am pretty sure we will hear about that when that happens. And act
> accordingly.
> 
>> The other option I can think of to not hurt your eyes is to rewrite the whole
>> page_ext_init(), init_page_owner(), init_debug_guardpage() to use all early
>> functions, so it can work in both with DEFERRED_STRUCT_PAGE_INIT=y and without.
>> However, I have a hard-time to convince myself it is a sensible thing to do.
> 
> Or simply make the page_owner initialization only touch the already
> initialized memory. Have you explored that option as well?

Yes, a proof-of-concept version is v1 where ends up with more ifdefs due to
dealing with all the low-level details,

https://lore.kernel.org/lkml/20181220060303.38686-1-cai@lca.pw/