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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
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 <20190103202235.GE31793@dhcp22.suse.cz>
From:   Qian Cai <cai@lca.pw>
Message-ID: <a5666d82-b7ad-4b90-5f4e-fd22afc3e1dc@lca.pw>
Date:   Thu, 3 Jan 2019 17:22:29 -0500
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On 1/3/19 3:22 PM, Michal Hocko wrote:
> On Thu 03-01-19 14:53:47, Qian Cai wrote:
>> On 1/3/19 2:07 PM, Michal Hocko wrote> So can we make the revert with an
>> explanation that the patch was wrong?
>>> If we want to make hacks to catch more objects to be tracked then it
>>> would be great to have some numbers in hands.
>>
>> Well, those numbers are subject to change depends on future start_kernel()
>> order. Right now, there are many functions could be caught earlier by page owner.
>>
>> 	kmemleak_init();
> [...]
>> 	sched_init_smp();
> 
> The kernel source dump will not tell us much of course. A ball park
> number whether we are talking about dozen, hundreds or thousands of
> allocations would tell us something at least, doesn't it.
> 
> Handwaving that it might help us some is not particurarly useful. We are
> already losing some allocations already. Does it matter? Well, that
> depends, sometimes we do want to catch an owner of particular page and
> it is sad to find nothing. But how many times have you or somebody else
> encountered that in practice. That is exactly a useful information to
> judge an ugly ifdefery in the code. See my point?

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.