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From: Zi Yan <ziy@nvidia.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>,
	Matthew Wilcox <willy@infradead.org>,
	Vlastimil Babka <vbabka@suse.cz>
Cc: <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Michal Hocko <mhocko@kernel.org>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	John Hubbard <jhubbard@nvidia.com>,
	Mark Hairgrove <mhairgrove@nvidia.com>,
	Nitin Gupta <nigupta@nvidia.com>,
	David Nellans <dnellans@nvidia.com>
Subject: Re: [RFC PATCH 01/31] mm: migrate: Add exchange_pages to exchange two lists of pages.
Date: Wed, 13 Mar 2019 19:39:26 -0700
Message-ID: <AD3BCC61-6604-4599-8A72-381A06122D2D@nvidia.com> (raw)
In-Reply-To: <749d5674-9e85-1fe9-4a3b-1d6ad06948b4@arm.com>

On 19 Feb 2019, at 20:38, Anshuman Khandual wrote:

> On 02/19/2019 06:26 PM, Matthew Wilcox wrote:
>> On Tue, Feb 19, 2019 at 01:12:07PM +0530, Anshuman Khandual wrote:
>>> But the location of this temp page matters as well because you would 
>>> like to
>>> saturate the inter node interface. It needs to be either of the 
>>> nodes where
>>> the source or destination page belongs. Any other node would 
>>> generate two
>>> internode copy process which is not what you intend here I guess.
>> That makes no sense.  It should be allocated on the local node of the 
>> CPU
>> performing the copy.  If the CPU is in node A, the destination is in 
>> node B
>> and the source is in node C, then you're doing 4k worth of reads from 
>> node C,
>> 4k worth of reads from node B, 4k worth of writes to node C followed 
>> by
>> 4k worth of writes to node B.  Eventually the 4k of dirty cachelines 
>> on
>> node A will be written back from cache to the local memory (... or 
>> not,
>> if that page gets reused for some other purpose first).
>>
>> If you allocate the page on node B or node C, that's an extra 4k of 
>> writes
>> to be sent across the inter-node link.
>
> Thats right there will be an extra remote write. My assumption was 
> that the CPU
> performing the copy belongs to either node B or node C.


I have some interesting throughput results for exchange per u64 and 
exchange per 4KB page.
What I discovered is that using a 4KB page as the temporary storage for 
exchanging
2MB THPs does not improve the throughput. On contrary, when we are 
exchanging more than 2^4=16 THPs,
exchanging per 4KB page has lower throughput than exchanging per u64. 
Please see results below.

The experiments are done on a two socket machine with two Intel Xeon 
E5-2640 v3 CPUs.
All exchanges are done via the QPI link across two sockets.


Results
===

Throughput (GB/s) of exchanging 2 order-N 2MB pages between two NUMA 
nodes

| 2mb_page_order | 0    | 1    | 2    | 3    | 4    | 5    | 6    | 7    
| 8    | 9
|     u64        | 5.31 | 5.58 | 5.89 | 5.69 | 8.97 | 9.51 | 9.21 | 9.50 
| 9.57 | 9.62
|     per_page   | 5.85 | 6.48 | 6.20 | 5.26 | 7.22 | 7.25 | 7.28 | 7.30 
| 7.32 | 7.31

Normalized throughput (to per_page)

  2mb_page_order | 0    | 1    | 2    | 3    | 4    | 5    | 6    | 7    
| 8    | 9
      u64        | 0.90 | 0.86 | 0.94 | 1.08 | 1.24 | 1.31 |1.26  | 1.30 
| 1.30 | 1.31



Exchange page code
===

For exchanging per u64, I use the following function:

static void exchange_page(char *to, char *from)
{
	u64 tmp;
	int i;

	for (i = 0; i < PAGE_SIZE; i += sizeof(tmp)) {
		tmp = *((u64 *)(from + i));
		*((u64 *)(from + i)) = *((u64 *)(to + i));
		*((u64 *)(to + i)) = tmp;
	}
}


For exchange per 4KB, I use the following function:

static void exchange_page2(char *to, char *from)
{
	int cpu = smp_processor_id();

	VM_BUG_ON(!in_atomic());

	if (!page_tmp[cpu]) {
		int nid = cpu_to_node(cpu);
		struct page *page_tmp_page = alloc_pages_node(nid, GFP_KERNEL, 0);
		if (!page_tmp_page) {
			exchange_page(to, from);
			return;
		}
		page_tmp[cpu] = kmap(page_tmp_page);
	}

	copy_page(page_tmp[cpu], to);
	copy_page(to, from);
	copy_page(from, page_tmp[cpu]);
}

where page_tmp is pre-allocated local to each CPU and alloc_pages_node() 
above
is for hot-added CPUs, which is not used in the tests.


The kernel is available at: https://gitlab.com/ziy/linux-contig-mem-rfc
To do a comparison, you can clone this repo: 
https://gitlab.com/ziy/thp-migration-bench,
then make, ./run_test.sh, and ./get_results.sh using the kernel from 
above.

Let me know if I missed anything or did something wrong. Thanks.


--
Best Regards,
Yan Zi


  reply index

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-15 22:08 [RFC PATCH 00/31] Generating physically contiguous memory after page allocation Zi Yan
2019-02-15 22:08 ` [RFC PATCH 01/31] mm: migrate: Add exchange_pages to exchange two lists of pages Zi Yan
2019-02-17 11:29   ` Matthew Wilcox
2019-02-18 17:31     ` Zi Yan
2019-02-18 17:42       ` Vlastimil Babka
2019-02-18 17:51         ` Zi Yan
2019-02-18 17:52           ` Matthew Wilcox
2019-02-18 17:59             ` Zi Yan
2019-02-19  7:42               ` Anshuman Khandual
2019-02-19 12:56                 ` Matthew Wilcox
2019-02-20  4:38                   ` Anshuman Khandual
2019-03-14  2:39                     ` Zi Yan [this message]
2019-02-21 21:10   ` Jerome Glisse
2019-02-21 21:25     ` Zi Yan
2019-02-15 22:08 ` [RFC PATCH 02/31] mm: migrate: Add THP exchange support Zi Yan
2019-02-15 22:08 ` [RFC PATCH 03/31] mm: migrate: Add tmpfs " Zi Yan
2019-02-15 22:08 ` [RFC PATCH 04/31] mm: add mem_defrag functionality Zi Yan
2019-02-15 22:08 ` [RFC PATCH 05/31] mem_defrag: split a THP if either src or dst is THP only Zi Yan
2019-02-15 22:08 ` [RFC PATCH 06/31] mm: Make MAX_ORDER configurable in Kconfig for buddy allocator Zi Yan
2019-02-15 22:08 ` [RFC PATCH 07/31] mm: deallocate pages with order > MAX_ORDER Zi Yan
2019-02-15 22:08 ` [RFC PATCH 08/31] mm: add pagechain container for storing multiple pages Zi Yan
2019-02-15 22:08 ` [RFC PATCH 09/31] mm: thp: 1GB anonymous page implementation Zi Yan
2019-02-15 22:08 ` [RFC PATCH 10/31] mm: proc: add 1GB THP kpageflag Zi Yan
2019-02-15 22:08 ` [RFC PATCH 11/31] mm: debug: print compound page order in dump_page() Zi Yan
2019-02-15 22:08 ` [RFC PATCH 12/31] mm: stats: Separate PMD THP and PUD THP stats Zi Yan
2019-02-15 22:08 ` [RFC PATCH 13/31] mm: thp: 1GB THP copy on write implementation Zi Yan
2019-02-15 22:08 ` [RFC PATCH 14/31] mm: thp: handling 1GB THP reference bit Zi Yan
2019-02-15 22:08 ` [RFC PATCH 15/31] mm: thp: add 1GB THP split_huge_pud_page() function Zi Yan
2019-02-15 22:08 ` [RFC PATCH 16/31] mm: thp: check compound_mapcount of PMD-mapped PUD THPs at free time Zi Yan
2019-02-15 22:08 ` [RFC PATCH 17/31] mm: thp: split properly PMD-mapped PUD THP to PTE-mapped PUD THP Zi Yan
2019-02-15 22:08 ` [RFC PATCH 18/31] mm: page_vma_walk: teach it about PMD-mapped " Zi Yan
2019-02-15 22:08 ` [RFC PATCH 19/31] mm: thp: 1GB THP support in try_to_unmap() Zi Yan
2019-02-15 22:08 ` [RFC PATCH 20/31] mm: thp: split 1GB THPs at page reclaim Zi Yan
2019-02-15 22:08 ` [RFC PATCH 21/31] mm: thp: 1GB zero page shrinker Zi Yan
2019-02-15 22:08 ` [RFC PATCH 22/31] mm: thp: 1GB THP follow_p*d_page() support Zi Yan
2019-02-15 22:08 ` [RFC PATCH 23/31] mm: support 1GB THP pagemap support Zi Yan
2019-02-15 22:08 ` [RFC PATCH 24/31] sysctl: add an option to only print the head page virtual address Zi Yan
2019-02-15 22:08 ` [RFC PATCH 25/31] mm: thp: add a knob to enable/disable 1GB THPs Zi Yan
2019-02-15 22:08 ` [RFC PATCH 26/31] mm: thp: promote PTE-mapped THP to PMD-mapped THP Zi Yan
2019-02-15 22:08 ` [RFC PATCH 27/31] mm: thp: promote PMD-mapped PUD pages to PUD-mapped PUD pages Zi Yan
2019-02-15 22:08 ` [RFC PATCH 28/31] mm: vmstats: add page promotion stats Zi Yan
2019-02-15 22:08 ` [RFC PATCH 29/31] mm: madvise: add madvise options to split PMD and PUD THPs Zi Yan
2019-02-15 22:08 ` [RFC PATCH 30/31] mm: mem_defrag: thp: PMD THP and PUD THP in-place promotion support Zi Yan
2019-02-15 22:08 ` [RFC PATCH 31/31] sysctl: toggle to promote PUD-mapped 1GB THP or not Zi Yan
2019-02-20  1:42 ` [RFC PATCH 00/31] Generating physically contiguous memory after page allocation Mike Kravetz
2019-02-20  2:33   ` Zi Yan
2019-02-20  3:18     ` Mike Kravetz
2019-02-20  5:19       ` Zi Yan
2019-02-20  5:27         ` Mike Kravetz
  -- strict thread matches above, loose matches on Subject: below --
2019-02-15 22:03 Zi Yan
2019-02-15 22:03 ` [RFC PATCH 01/31] mm: migrate: Add exchange_pages to exchange two lists of pages Zi Yan

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