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Date:   Wed, 27 Jun 2018 09:47:57 +0800
From:   Baoquan He <bhe@redhat.com>
To:     linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
        dave.hansen@intel.com, pagupta@redhat.com
Cc:     linux-mm@kvack.org, kirill.shutemov@linux.intel.com
Subject: Re: [PATCH v5 0/4] mm/sparse: Optimize memmap allocation during
 sparse_init()
Message-ID: <20180627014757.GC8970@localhost.localdomain>
References: <20180627013116.12411-1-bhe@redhat.com>
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On 06/27/18 at 09:31am, Baoquan He wrote:
> This is v4 post. V3 can be found here:
> https://lkml.org/lkml/2018/2/27/928

Sorry, forgot updating this part.

This is v5 post, v4 can be found here:
http://lkml.kernel.org/r/20180521101555.25610-1-bhe@redhat.com

> 
> 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.
> 
> Change log:
> v4->v5:
>   Improve patch 3/4 log according to Dave's suggestion.
> 
>   Correct the wrong copy&paste of making 'nr_consumed_maps' to
>   'alloc_usemap_and_memmap' mistakenly which is pointed out by
>   Dave in patch 4/4 code comment.
> 
>   Otherwise, no code change in this version.
> v3->v4:
>   Improve according to Dave's three concerns which are in patch 0004:
> 
>   Rename variable 'idx_present' to 'nr_consumed_maps' which used to
>   index the memmap and usemap of present sections.
> 
>   Add a check if 'nr_consumed_maps' goes beyond nr_present_sections.
> 
>   Add code comment above the final for_each_present_section_nr() to
>   tell why 'nr_consumed_maps' need be increased in each iteration
>   whether the 'ms->section_mem_map' need cleared or out.
> 
> v2->v3:
>   Change nr_present_sections as __initdata and add code comment
>   according to Andrew's suggestion.
> 
>   Change the local variable 'i' as idx_present which loops over the
>   present sections, and improve the code. These are suggested by
>   Dave and Pankaj.
> 
>   Add a new patch 0003 which adds a new parameter 'data_unit_size'
>   to function alloc_usemap_and_memmap() in which we will update 'data'
>   to make it point at new position. However its type 'void *' can't give
>   us needed info to do that. Need pass the unit size in. So change code
>   in patch 0004 accordingly. This is a code bug fix found when tested
>   the memory deployed on multiple nodes.
> 
> v1-v2:
>   Split out the nr_present_sections adding as a single patch for easier
>   reviewing.
> 
>   Rewrite patch log according to Dave's suggestion.
> 
>   Fix code bug in patch 0002 reported by test robot.
> 
> Baoquan He (4):
>   mm/sparse: Add a static variable nr_present_sections
>   mm/sparsemem: Defer the ms->section_mem_map clearing
>   mm/sparse: Add a new parameter 'data_unit_size' for
>     alloc_usemap_and_memmap
>   mm/sparse: Optimize memmap allocation during sparse_init()
> 
>  mm/sparse-vmemmap.c |  6 ++---
>  mm/sparse.c         | 72 +++++++++++++++++++++++++++++++++++++++++------------
>  2 files changed, 59 insertions(+), 19 deletions(-)
> 
> -- 
> 2.13.6
>