linux-kernel - Re: [v2 PATCH] mm: move page_ext_init after all struct pages are initialized

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Message-ID: <dfdab52b-f6dc-b72a-58a3-2884aaa2254c@linaro.org>
Date:	Mon, 23 May 2016 09:42:00 -0700
From:	"Shi, Yang" <yang.shi@...aro.org>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	akpm@...ux-foundation.org, iamjoonsoo.kim@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linaro-kernel@...ts.linaro.org
Subject: Re: [v2 PATCH] mm: move page_ext_init after all struct pages are
 initialized

On 5/23/2016 12:31 AM, Michal Hocko wrote:
> On Fri 20-05-16 08:41:09, Shi, Yang wrote:
>> On 5/20/2016 6:16 AM, Michal Hocko wrote:
>>> On Thu 19-05-16 15:13:26, Yang Shi wrote:
>>> [...]
>>>> diff --git a/init/main.c b/init/main.c
>>>> index b3c6e36..2075faf 100644
>>>> --- a/init/main.c
>>>> +++ b/init/main.c
>>>> @@ -606,7 +606,6 @@ asmlinkage __visible void __init start_kernel(void)
>>>>  		initrd_start = 0;
>>>>  	}
>>>>  #endif
>>>> -	page_ext_init();
>>>>  	debug_objects_mem_init();
>>>>  	kmemleak_init();
>>>>  	setup_per_cpu_pageset();
>>>> @@ -1004,6 +1003,8 @@ static noinline void __init kernel_init_freeable(void)
>>>>  	sched_init_smp();
>>>>
>>>>  	page_alloc_init_late();
>>>> +	/* Initialize page ext after all struct pages are initializaed */
>>>> +	page_ext_init();
>>>>
>>>>  	do_basic_setup();
>>>
>>> I might be missing something but don't we have the same problem with
>>> CONFIG_FLATMEM? page_ext_init_flatmem is called way earlier. Or
>>> CONFIG_DEFERRED_STRUCT_PAGE_INIT is never enabled for CONFIG_FLATMEM?
>>
>> Yes, CONFIG_DEFERRED_STRUCT_PAGE_INIT depends on MEMORY_HOTPLUG which
>> depends on SPARSEMEM. So, this config is not valid for FLATMEM at all.
>
> Well
> config MEMORY_HOTPLUG
>         bool "Allow for memory hot-add"
> 	depends on SPARSEMEM || X86_64_ACPI_NUMA
> 	depends on ARCH_ENABLE_MEMORY_HOTPLUG
>
> I wasn't really sure about X86_64_ACPI_NUMA dependency branch which
> depends on X86_64 && NUMA && ACPI && PCI and that didn't sound like
> SPARSEMEM only. If the FLATMEM shouldn't exist with

Actually, FLATMEMT depends on !NUMA.

> CONFIG_DEFERRED_STRUCT_PAGE_INIT can we make that explicit please?

Sure, it makes the condition clearer and more readable.

Thanks,
Yang

>