linux-kernel - Re: [PATCH v5 0/5] sparse

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Date:   Fri, 13 Jul 2018 11:59:34 +0200
From:   Oscar Salvador <osalvador@...hadventures.net>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        kirill.shutemov@...ux.intel.com, mhocko@...e.com,
        linux-mm@...ck.org, dan.j.williams@...el.com, jack@...e.cz,
        jglisse@...hat.com, jrdr.linux@...il.com, bhe@...hat.com,
        gregkh@...uxfoundation.org, vbabka@...e.cz,
        richard.weiyang@...il.com, dave.hansen@...el.com,
        rientjes@...gle.com, mingo@...nel.org, abdhalee@...ux.vnet.ibm.com,
        mpe@...erman.id.au
Subject: Re: [PATCH v5 0/5] sparse_init rewrite

On Thu, Jul 12, 2018 at 04:37:25PM -0400, Pavel Tatashin wrote:
> Changelog:
> v5 - v4
> 	- Fixed the issue that was reported on ppc64 when
> 	  CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER is removed
> 	- Consolidated the new buffer allocation between vmemmap
> 	  and non-vmemmap variants of sparse layout.
> 	- Removed all review-by comments, because I had to do
> 	  significant amount of changes compared to previous version
> 	  and need another round of review.
> 	- I also would appreciate if those who reported problems with
> 	  PPC64 could test this change.

About PPC64, your patchset fixes the issue as the population gets followed by a
sparse_init_one_section().

It can be seen here:

Before:

kernel: vmemmap_populate f000000000000000..f000000000004000, node 0
kernel:       * f000000000000000..f000000000010000 allocated at (____ptrval____)
kernel: vmemmap_populate f000000000000000..f000000000008000, node 0
kernel:       * f000000000000000..f000000000010000 allocated at (____ptrval____)
kernel: vmemmap_populate f000000000000000..f00000000000c000, node 0
kernel:       * f000000000000000..f000000000010000 allocated at (____ptrval____)


After:

kernel: vmemmap_populate f000000000000000..f000000000004000, node 0
kernel:       * f000000000000000..f000000000010000 allocated at (____ptrval____)
kernel: vmemmap_populate f000000000000000..f000000000008000, node 0
kernel: vmemmap_populate f000000000000000..f00000000000c000, node 0
kernel: vmemmap_populate f000000000000000..f000000000010000, node 0
kernel: vmemmap_populate f000000000010000..f000000000014000, node 0
kernel:       * f000000000010000..f000000000020000 allocated at (____ptrval____)


As can be seen, before the patchset, we keep calling vmemmap_create_mapping() even if we
populated that section already, because of vmemmap_populated() checking for SECTION_HAS_MEM_MAP.

After the patchset, since each population is being followed by a call to sparse_init_one_section(),
when vmemmap_populated() gets called, we have SECTION_HAS_MEM_MAP already in case the section
was populated.
-- 
Oscar Salvador
SUSE L3