linux-kernel - Re: [tip:x86/mm] mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM

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Date:   Thu, 2 Nov 2017 15:07:27 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>, hpa@...or.com,
        Andrew Morton <akpm@...ux-foundation.org>, gorcunov@...nvz.org,
        luto@...capital.net, bp@...e.de,
        open list <linux-kernel@...r.kernel.org>,
        torvalds@...ux-foundation.org, Will Deacon <Will.Deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [tip:x86/mm] mm/sparsemem: Allocate mem_section at runtime for
 CONFIG_SPARSEMEM_EXTREME=y



On 02/11/17 14:12, Kirill A. Shutemov wrote:
> On Thu, Nov 02, 2017 at 01:42:42PM +0000, Sudeep Holla wrote:
>>
>>
>> On 02/11/17 13:34, Kirill A. Shutemov wrote:
>>> On Thu, Nov 02, 2017 at 12:31:54PM +0000, Sudeep Holla wrote:
>>>> (+Will, Catalin)
>>>>
>>>> On Fri, Oct 20, 2017 at 1:27 PM, tip-bot for Kirill A. Shutemov
>>>> <tipbot@...or.com> wrote:
>>>>> Commit-ID:  83e3c48729d9ebb7af5a31a504f3fd6aff0348c4
>>>>> Gitweb:     https://git.kernel.org/tip/83e3c48729d9ebb7af5a31a504f3fd6aff0348c4
>>>>> Author:     Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>>>>> AuthorDate: Fri, 29 Sep 2017 17:08:16 +0300
>>>>> Committer:  Ingo Molnar <mingo@...nel.org>
>>>>> CommitDate: Fri, 20 Oct 2017 13:07:09 +0200
>>>>>
>>>>> mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y
>>>>>
>>>>> Size of the mem_section[] array depends on the size of the physical address space.
>>>>>
>>>>> In preparation for boot-time switching between paging modes on x86-64
>>>>> we need to make the allocation of mem_section[] dynamic, because otherwise
>>>>> we waste a lot of RAM: with CONFIG_NODE_SHIFT=10, mem_section[] size is 32kB
>>>>> for 4-level paging and 2MB for 5-level paging mode.
>>>>>
>>>>> The patch allocates the array on the first call to sparse_memory_present_with_active_regions().
>>>>>
>>>>
>>>> I am seeing a boot failure with this patch in linux-next today(20171102)
>>>
>>> Could you share the kernel config?
>>>
>>
>> It's the default config on arm64. Generated file is almost 160kB, I will
>> send it to you off-list.
>>
>>> Have you bisected the failure to the commit?
>>>
>> I just reverted this commit as I suspected that and it boots fine after
>> the revert.
> 
> Could you try the patch below instead?
> 
> From 4a9d843f9d939d958612b0079ebe5743f265e1e0 Mon Sep 17 00:00:00 2001
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> Date: Thu, 2 Nov 2017 17:02:29 +0300
> Subject: [PATCH] mm, sparse: Fix boot on arm64
> 
> Since 83e3c48729d9 ("mm/sparsemem: Allocate mem_section at runtime for
> CONFIG_SPARSEMEM_EXTREME=y") we allocate mem_section dynamically in
> sparse_memory_present_with_active_regions(). But some architectures, like
> arm64, don't use the routine to initialize sparsemem.
> 
> Let's move the initialization into memory_present() it should cover all
> architectures.
> 

Thanks for the quick fix. It boots fine with this patch.

Reported-and-tested-by: Sudeep Holla <sudeep.holla@....com>

-- 
Regards,
Sudeep