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 16:37:29 +0100
From:   Thierry Reding <thierry.reding@...il.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 Thu, Nov 02, 2017 at 05:12:11PM +0300, 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.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Fixes: 83e3c48729d9 ("mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y")
> ---
>  mm/page_alloc.c | 10 ----------
>  mm/sparse.c     | 10 ++++++++++
>  2 files changed, 10 insertions(+), 10 deletions(-)

I can also confirm that this restores booting on 64-bit ARM (Tegra186,
Jetson TX2, specifically):

Tested-by: Thierry Reding <treding@...dia.com>

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