linux-kernel - Re: [PATCH v3 0/4] mm/sparse: Optimize memmap allocation during sparse

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Message-Id: <20180405150842.350e4febc06a813138f00416@linux-foundation.org>
Date:   Thu, 5 Apr 2018 15:08:42 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     linux-kernel@...r.kernel.org, dave.hansen@...el.com,
        pagupta@...hat.com, linux-mm@...ck.org,
        kirill.shutemov@...ux.intel.com
Subject: Re: [PATCH v3 0/4] mm/sparse: Optimize memmap allocation during
 sparse_init()

On Wed, 28 Feb 2018 11:26:53 +0800 Baoquan He <bhe@...hat.com> wrote:

> This is v3 post. V1 can be found here:
> https://www.spinics.net/lists/linux-mm/msg144486.html
> 
> In sparse_init(), two temporary pointer arrays, usemap_map and map_map
> are allocated with the size of NR_MEM_SECTIONS. They are used to store
> each memory section's usemap and mem map if marked as present. In
> 5-level paging mode, this will cost 512M memory though they will be
> released at the end of sparse_init(). System with few memory, like
> kdump kernel which usually only has about 256M, will fail to boot
> because of allocation failure if CONFIG_X86_5LEVEL=y.
> 
> In this patchset, optimize the memmap allocation code to only use
> usemap_map and map_map with the size of nr_present_sections. This
> makes kdump kernel boot up with normal crashkernel='' setting when
> CONFIG_X86_5LEVEL=y.

This patchset could do with some more review, please?