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    SubjectRe: [tip:x86/mm] mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y
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    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@zytor.com> wrote:
    >>>>> Commit-ID: 83e3c48729d9ebb7af5a31a504f3fd6aff0348c4
    >>>>> Gitweb: https://git.kernel.org/tip/83e3c48729d9ebb7af5a31a504f3fd6aff0348c4
    >>>>> Author: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    >>>>> AuthorDate: Fri, 29 Sep 2017 17:08:16 +0300
    >>>>> Committer: Ingo Molnar <mingo@kernel.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@linux.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@arm.com>

    --
    Regards,
    Sudeep

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