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From: Zi Yan <ziy@nvidia.com>
To: Matthew Wilcox <willy@infradead.org>
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>,
	Vlastimil Babka <vbabka@suse.cz>,
	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: Mon, 18 Feb 2019 09:31:24 -0800
Message-ID: <65A1FFA0-531C-4078-9704-3F44819C3C07@nvidia.com> (raw)
In-Reply-To: <20190217112943.GP12668@bombadil.infradead.org>

On 17 Feb 2019, at 3:29, Matthew Wilcox wrote:

> On Fri, Feb 15, 2019 at 02:08:26PM -0800, Zi Yan wrote:
>> +struct page_flags {
>> +	unsigned int page_error :1;
>> +	unsigned int page_referenced:1;
>> +	unsigned int page_uptodate:1;
>> +	unsigned int page_active:1;
>> +	unsigned int page_unevictable:1;
>> +	unsigned int page_checked:1;
>> +	unsigned int page_mappedtodisk:1;
>> +	unsigned int page_dirty:1;
>> +	unsigned int page_is_young:1;
>> +	unsigned int page_is_idle:1;
>> +	unsigned int page_swapcache:1;
>> +	unsigned int page_writeback:1;
>> +	unsigned int page_private:1;
>> +	unsigned int __pad:3;
>> +};
>
> I'm not sure how to feel about this.  It's a bit fragile versus 
> somebody adding
> new page flags.  I don't know whether it's needed or whether you can 
> just
> copy page->flags directly because you're holding PageLock.

I agree with you that current way of copying page flags individually 
could miss
new page flags. I will try to come up with something better. Copying 
page->flags as a whole
might not simply work, since the upper part of page->flags has the page 
node information,
which should not be changed. I think I need to add a helper function to 
just copy/exchange
all page flags, like calling migrate_page_stats() twice.

>> +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;
>> +	}
>> +}
>
> I have a suspicion you'd be better off allocating a temporary page and
> using copy_page().  Some architectures have put a lot of effort into
> making copy_page() run faster.

When I am doing exchange_pages() between two NUMA nodes on a x86_64 
machine,
I actually can saturate the QPI bandwidth with this operation. I think 
cache
prefetching was doing its job.

The purpose of proposing exchange_pages() is to avoid allocating any new 
page,
so that we would not trigger any potential page reclaim or memory 
compaction.
Allocating a temporary page defeats the purpose.

>
>> +		xa_lock_irq(&to_mapping->i_pages);
>> +
>> +		to_pslot = radix_tree_lookup_slot(&to_mapping->i_pages,
>> +			page_index(to_page));
>
> This needs to be converted to the XArray.  radix_tree_lookup_slot() is
> going away soon.  You probably need:
>
> 	XA_STATE(to_xas, &to_mapping->i_pages, page_index(to_page));

Thank you for pointing this out. I will do the change.

>
> This is a lot of code and I'm still trying to get my head aroud it 
> all.
> Thanks for putting in this work; it's good to see this approach being
> explored.

Thank you for taking a look at the code.

--
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 [this message]
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
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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