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

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Message-ID: <87bmb7znrx.fsf@concordia.ellerman.id.au>
Date:   Mon, 16 Jul 2018 16:40:34 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>,
        osalvador@...hadventures.net
Cc:     Steven Sistare <steven.sistare@...cle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kirill.shutemov@...ux.intel.com, Michal Hocko <mhocko@...e.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        dan.j.williams@...el.com, jack@...e.cz, jglisse@...hat.com,
        Souptick Joarder <jrdr.linux@...il.com>, bhe@...hat.com,
        gregkh@...uxfoundation.org, Vlastimil Babka <vbabka@...e.cz>,
        Wei Yang <richard.weiyang@...il.com>, dave.hansen@...el.com,
        rientjes@...gle.com, mingo@...nel.org, abdhalee@...ux.vnet.ibm.com
Subject: Re: [PATCH v5 0/5] sparse_init rewrite

Pavel Tatashin <pasha.tatashin@...cle.com> writes:

>> 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.
>
> Hi Oscar,
>
> Right, I also like that this solution removes one extra loop, thus
> reduces the code size. We were populating pages in one place, and then
> loop again to set sections, now we do both in one place, but still
> allow preallocation of memory to reduces fragmentation on all
> platforms. However, I still wanted to see if someone could test on
> real hardware.

I booted it on a small VM and a 160 CPU 4 node machine, both booted
fine.

If you want:
  Tested-by: Michael Ellerman <mpe@...erman.id.au> (powerpc)


Thanks for fixing it up for us.

cheers