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[v1 0/5] parallelized "struct page" zeroing

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  [v1 0/5] parallelized "struct page" zeroing Pavel Tatashin <pasha.tatashin@oracle.com> - 2017-03-24 00:00 +0100
    Re: [v1 0/5] parallelized "struct page" zeroing Matthew Wilcox <willy@infradead.org> - 2017-03-24 00:30 +0100
      Re: [v1 0/5] parallelized "struct page" zeroing Pasha Tatashin <pasha.tatashin@oracle.com> - 2017-03-24 00:40 +0100
      Re: [v1 0/5] parallelized "struct page" zeroing David Miller <davem@davemloft.net> - 2017-03-24 00:40 +0100
        Re: [v1 0/5] parallelized "struct page" zeroing Pasha Tatashin <pasha.tatashin@oracle.com> - 2017-03-24 00:50 +0100
          Re: [v1 0/5] parallelized "struct page" zeroing Pasha Tatashin <pasha.tatashin@oracle.com> - 2017-03-24 02:20 +0100
    Re: [v1 0/5] parallelized "struct page" zeroing Christian Borntraeger <borntraeger@de.ibm.com> - 2017-03-24 10:00 +0100
      Re: [v1 0/5] parallelized "struct page" zeroing Heiko Carstens <heiko.carstens@de.ibm.com> - 2017-03-24 10:40 +0100

#1608011 — [v1 0/5] parallelized "struct page" zeroing

When deferred struct page initialization feature is enabled, we get a
performance gain of initializing vmemmap in parallel after other CPUs are
started. However, we still zero the memory for vmemmap using one boot CPU.
This patch-set fixes the memset-zeroing limitation by deferring it as well.

Here is example performance gain on SPARC with 32T:
base
https://hastebin.com/ozanelatat.go

fix
https://hastebin.com/utonawukof.go

As you can see without the fix it takes: 97.89s to boot
With the fix it takes: 46.91 to boot.

On x86 time saving is going to be even greater (proportionally to memory size)
because there are twice as many "struct page"es for the same amount of memory,
as base pages are twice smaller.


Pavel Tatashin (5):
  sparc64: simplify vmemmap_populate
  mm: defining memblock_virt_alloc_try_nid_raw
  mm: add "zero" argument to vmemmap allocators
  mm: zero struct pages during initialization
  mm: teach platforms not to zero struct pages memory

 arch/powerpc/mm/init_64.c |    4 +-
 arch/s390/mm/vmem.c       |    5 ++-
 arch/sparc/mm/init_64.c   |   26 +++++++----------------
 arch/x86/mm/init_64.c     |    3 +-
 include/linux/bootmem.h   |    3 ++
 include/linux/mm.h        |   15 +++++++++++--
 mm/memblock.c             |   46 ++++++++++++++++++++++++++++++++++++------
 mm/page_alloc.c           |    3 ++
 mm/sparse-vmemmap.c       |   48 +++++++++++++++++++++++++++++---------------
 9 files changed, 103 insertions(+), 50 deletions(-)

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#1608013

On Thu, Mar 23, 2017 at 07:01:48PM -0400, Pavel Tatashin wrote:
> When deferred struct page initialization feature is enabled, we get a
> performance gain of initializing vmemmap in parallel after other CPUs are
> started. However, we still zero the memory for vmemmap using one boot CPU.
> This patch-set fixes the memset-zeroing limitation by deferring it as well.
> 
> Here is example performance gain on SPARC with 32T:
> base
> https://hastebin.com/ozanelatat.go
> 
> fix
> https://hastebin.com/utonawukof.go
> 
> As you can see without the fix it takes: 97.89s to boot
> With the fix it takes: 46.91 to boot.

How long does it take if we just don't zero this memory at all?  We seem
to be initialising most of struct page in __init_single_page(), so it
seems like a lot of additional complexity to conditionally zero the rest
of struct page.

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#1608014

Hi Matthew,

Thank you for your comment. If you look at the data, having memset() 
actually benefits initializing data.

With base it takes:
[   66.148867] node 0 initialised, 128312523 pages in 7200ms

With fix:
[   15.260634] node 0 initialised, 128312523 pages in 4190ms

So 4.19s vs 7.2s for the same number of "struct page". This is because 
memset() actually brings "struct page" into cache with efficient  block 
initializing store instruction. I have not tested if there is the same 
effect on Intel.

Pasha

On 03/23/2017 07:26 PM, Matthew Wilcox wrote:
> On Thu, Mar 23, 2017 at 07:01:48PM -0400, Pavel Tatashin wrote:
>> When deferred struct page initialization feature is enabled, we get a
>> performance gain of initializing vmemmap in parallel after other CPUs are
>> started. However, we still zero the memory for vmemmap using one boot CPU.
>> This patch-set fixes the memset-zeroing limitation by deferring it as well.
>>
>> Here is example performance gain on SPARC with 32T:
>> base
>> https://hastebin.com/ozanelatat.go
>>
>> fix
>> https://hastebin.com/utonawukof.go
>>
>> As you can see without the fix it takes: 97.89s to boot
>> With the fix it takes: 46.91 to boot.
>
> How long does it take if we just don't zero this memory at all?  We seem
> to be initialising most of struct page in __init_single_page(), so it
> seems like a lot of additional complexity to conditionally zero the rest
> of struct page.
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
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> see: http://www.linux-mm.org/ .
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>

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#1608016

From: Matthew Wilcox <willy@infradead.org>
Date: Thu, 23 Mar 2017 16:26:38 -0700

> On Thu, Mar 23, 2017 at 07:01:48PM -0400, Pavel Tatashin wrote:
>> When deferred struct page initialization feature is enabled, we get a
>> performance gain of initializing vmemmap in parallel after other CPUs are
>> started. However, we still zero the memory for vmemmap using one boot CPU.
>> This patch-set fixes the memset-zeroing limitation by deferring it as well.
>> 
>> Here is example performance gain on SPARC with 32T:
>> base
>> https://hastebin.com/ozanelatat.go
>> 
>> fix
>> https://hastebin.com/utonawukof.go
>> 
>> As you can see without the fix it takes: 97.89s to boot
>> With the fix it takes: 46.91 to boot.
> 
> How long does it take if we just don't zero this memory at all?  We seem
> to be initialising most of struct page in __init_single_page(), so it
> seems like a lot of additional complexity to conditionally zero the rest
> of struct page.

Alternatively, just zero out the entire vmemmap area when it is setup
in the kernel page tables.

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#1608018

On 03/23/2017 07:35 PM, David Miller wrote:
> From: Matthew Wilcox <willy@infradead.org>
> Date: Thu, 23 Mar 2017 16:26:38 -0700
>
>> On Thu, Mar 23, 2017 at 07:01:48PM -0400, Pavel Tatashin wrote:
>>> When deferred struct page initialization feature is enabled, we get a
>>> performance gain of initializing vmemmap in parallel after other CPUs are
>>> started. However, we still zero the memory for vmemmap using one boot CPU.
>>> This patch-set fixes the memset-zeroing limitation by deferring it as well.
>>>
>>> Here is example performance gain on SPARC with 32T:
>>> base
>>> https://hastebin.com/ozanelatat.go
>>>
>>> fix
>>> https://hastebin.com/utonawukof.go
>>>
>>> As you can see without the fix it takes: 97.89s to boot
>>> With the fix it takes: 46.91 to boot.
>>
>> How long does it take if we just don't zero this memory at all?  We seem
>> to be initialising most of struct page in __init_single_page(), so it
>> seems like a lot of additional complexity to conditionally zero the rest
>> of struct page.
>
> Alternatively, just zero out the entire vmemmap area when it is setup
> in the kernel page tables.

Hi Dave,

I can do this, either way is fine with me. It would be a little slower 
compared to the current approach where we benefit from having memset() 
to work as prefetch. But that would become negligible, once in the 
future we will increase the granularity of multi-threading, currently it 
is only one thread per-mnode to multithread vmemamp. Your call.

Thank  you,
Pasha

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#1608060

On 03/23/2017 07:47 PM, Pasha Tatashin wrote:
>>>
>>> How long does it take if we just don't zero this memory at all?  We seem
>>> to be initialising most of struct page in __init_single_page(), so it
>>> seems like a lot of additional complexity to conditionally zero the rest
>>> of struct page.
>>
>> Alternatively, just zero out the entire vmemmap area when it is setup
>> in the kernel page tables.
>
> Hi Dave,
>
> I can do this, either way is fine with me. It would be a little slower
> compared to the current approach where we benefit from having memset()
> to work as prefetch. But that would become negligible, once in the
> future we will increase the granularity of multi-threading, currently it
> is only one thread per-mnode to multithread vmemamp. Your call.
>
> Thank  you,
> Pasha

Hi Dave and Matthew,

I've been thinking about it some more, and figured that the current 
approach is better:

1. Most importantly: Part of the vmemmap is initialized early during 
boot to support Linux to get to the multi-CPU environment. This means 
that we would need to figure out what part of vmemmap will need to be 
zeroed before hand in single thread, than zero the rest in multi-thread. 
This will be very awkward architecturally and error prone.

2. As I already showed, the current approach is significantly faster. 
So, perhaps it should be the default behavior even for non-deferred 
"struct page" initialization: unconditionally do not zero vmemmap in 
memblock allocator, and always zero in __init_single_page(). But, I am 
afraid it could cause boot time regressions on some platforms where 
memset() is not optimized, so I would not do it in this patchset. But, 
hopefully, gradually more platforms will support deferred struct page 
initialization, and this would become the default behavior.

3. By zeroing "struct page" in  __init_single_page(), we set every byte 
of "struct page" in one place instead of scattering it across different 
places. So, it could help in the future when we will multi-thread 
addition of hotplugged memory.

Thank you,
Pasha

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#1608233

On 03/24/2017 12:01 AM, Pavel Tatashin wrote:
> When deferred struct page initialization feature is enabled, we get a
> performance gain of initializing vmemmap in parallel after other CPUs are
> started. However, we still zero the memory for vmemmap using one boot CPU.
> This patch-set fixes the memset-zeroing limitation by deferring it as well.
> 
> Here is example performance gain on SPARC with 32T:
> base
> https://hastebin.com/ozanelatat.go
> 
> fix
> https://hastebin.com/utonawukof.go
> 
> As you can see without the fix it takes: 97.89s to boot
> With the fix it takes: 46.91 to boot.
> 
> On x86 time saving is going to be even greater (proportionally to memory size)
> because there are twice as many "struct page"es for the same amount of memory,
> as base pages are twice smaller.

Fixing the linux-s390 mailing list email.
This might be useful for s390 as well.

> 
> 
> Pavel Tatashin (5):
>   sparc64: simplify vmemmap_populate
>   mm: defining memblock_virt_alloc_try_nid_raw
>   mm: add "zero" argument to vmemmap allocators
>   mm: zero struct pages during initialization
>   mm: teach platforms not to zero struct pages memory
> 
>  arch/powerpc/mm/init_64.c |    4 +-
>  arch/s390/mm/vmem.c       |    5 ++-
>  arch/sparc/mm/init_64.c   |   26 +++++++----------------
>  arch/x86/mm/init_64.c     |    3 +-
>  include/linux/bootmem.h   |    3 ++
>  include/linux/mm.h        |   15 +++++++++++--
>  mm/memblock.c             |   46 ++++++++++++++++++++++++++++++++++++------
>  mm/page_alloc.c           |    3 ++
>  mm/sparse-vmemmap.c       |   48 +++++++++++++++++++++++++++++---------------
>  9 files changed, 103 insertions(+), 50 deletions(-)
> 

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#1608271

On Fri, Mar 24, 2017 at 09:51:09AM +0100, Christian Borntraeger wrote:
> On 03/24/2017 12:01 AM, Pavel Tatashin wrote:
> > When deferred struct page initialization feature is enabled, we get a
> > performance gain of initializing vmemmap in parallel after other CPUs are
> > started. However, we still zero the memory for vmemmap using one boot CPU.
> > This patch-set fixes the memset-zeroing limitation by deferring it as well.
> > 
> > Here is example performance gain on SPARC with 32T:
> > base
> > https://hastebin.com/ozanelatat.go
> > 
> > fix
> > https://hastebin.com/utonawukof.go
> > 
> > As you can see without the fix it takes: 97.89s to boot
> > With the fix it takes: 46.91 to boot.
> > 
> > On x86 time saving is going to be even greater (proportionally to memory size)
> > because there are twice as many "struct page"es for the same amount of memory,
> > as base pages are twice smaller.
> 
> Fixing the linux-s390 mailing list email.
> This might be useful for s390 as well.

Unfortunately only for the fake numa case, since as far as I understand it,
parallelization happens only on a node granularity. And since we are
usually only having one node...

But anyway, it won't hurt to set ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT on
s390 also. I'll do some testing and then we'll see.

Pavel, could you please change your patch 5 so it also converts the s390
call sites of vmemmap_alloc_block() so they use VMEMMAP_ZERO instead of
'true' as argument?

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