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From: Joao Martins <joao.m.martins@oracle.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: linux-mm@kvack.org, linux-nvdimm@lists.01.org,
	Matthew Wilcox <willy@infradead.org>,
	Muchun Song <songmuchun@bytedance.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH RFC 6/9] mm/gup: Grab head page refcount once for group of subpages
Date: Wed, 9 Dec 2020 11:05:39 +0000	[thread overview]
Message-ID: <b7f5fe44-f2f5-aea6-57b3-7e14a9ef624d@oracle.com> (raw)
In-Reply-To: <20201208194905.GQ5487@ziepe.ca>



On 12/8/20 7:49 PM, Jason Gunthorpe wrote:
> On Tue, Dec 08, 2020 at 05:28:58PM +0000, Joao Martins wrote:
>> Much like hugetlbfs or THPs, we treat device pagemaps with
>> compound pages like the rest of GUP handling of compound pages.
>>
>> Rather than incrementing the refcount every 4K, we record
>> all sub pages and increment by @refs amount *once*.
>>
>> Performance measured by gup_benchmark improves considerably
>> get_user_pages_fast() and pin_user_pages_fast():
>>
>>  $ gup_benchmark -f /dev/dax0.2 -m 16384 -r 10 -S [-u,-a] -n 512 -w
>>
>> (get_user_pages_fast 2M pages) ~75k us -> ~3.6k us
>> (pin_user_pages_fast 2M pages) ~125k us -> ~3.8k us
>>
>> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
>>  mm/gup.c | 67 ++++++++++++++++++++++++++++++++++++++++++--------------
>>  1 file changed, 51 insertions(+), 16 deletions(-)
>>
>> diff --git a/mm/gup.c b/mm/gup.c
>> index 98eb8e6d2609..194e6981eb03 100644
>> +++ b/mm/gup.c
>> @@ -2250,22 +2250,68 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
>>  }
>>  #endif /* CONFIG_ARCH_HAS_PTE_SPECIAL */
>>  
>> +
>> +static int record_subpages(struct page *page, unsigned long addr,
>> +			   unsigned long end, struct page **pages)
>> +{
>> +	int nr;
>> +
>> +	for (nr = 0; addr != end; addr += PAGE_SIZE)
>> +		pages[nr++] = page++;
>> +
>> +	return nr;
>> +}
>> +
>>  #if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
>> -static int __gup_device_huge(unsigned long pfn, unsigned long addr,
>> -			     unsigned long end, unsigned int flags,
>> -			     struct page **pages, int *nr)
>> +static int __gup_device_compound_huge(struct dev_pagemap *pgmap,
>> +				      struct page *head, unsigned long sz,
>> +				      unsigned long addr, unsigned long end,
>> +				      unsigned int flags, struct page **pages)
>> +{
>> +	struct page *page;
>> +	int refs;
>> +
>> +	if (!(pgmap->flags & PGMAP_COMPOUND))
>> +		return -1;
>> +
>> +	page = head + ((addr & (sz-1)) >> PAGE_SHIFT);
> 
> All the places that call record_subpages do some kind of maths like
> this, it should be placed inside record_subpages and not opencoded
> everywhere.
> 
Makes sense.

>> +	refs = record_subpages(page, addr, end, pages);
>> +
>> +	SetPageReferenced(page);
>> +	head = try_grab_compound_head(head, refs, flags);
>> +	if (!head) {
>> +		ClearPageReferenced(page);
>> +		return 0;
>> +	}
>> +
>> +	return refs;
>> +}
> 
> Why is all of this special? Any time we see a PMD/PGD/etc pointing to
> PFN we can apply this optimization. How come device has its own
> special path to do this?? 
> 
I think the reason is that zone_device struct pages have no relationship to one other. So
you anyways need to change individual pages, as opposed to just the head page.

I made it special to avoid breaking other ZONE_DEVICE users (and gating that with
PGMAP_COMPOUND). But if there's no concerns with that, I can unilaterally enable it.

> Why do we need to check PGMAP_COMPOUND? Why do we need to get pgmap?
> (We already removed that from the hmm version of this, was that wrong?
> Is this different?) Dan?
> 
> Also undo_dev_pagemap() is now out of date, we have unpin_user_pages()
> for that and no other error unwind touches ClearPageReferenced..
> 
/me nods Yeap I saw that too.

> Basic idea is good though!
> 
Cool, thanks!

	Joao
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WARNING: multiple messages have this Message-ID
From: Joao Martins <joao.m.martins@oracle.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: linux-mm@kvack.org, Dan Williams <dan.j.williams@intel.com>,
	Ira Weiny <ira.weiny@intel.com>,
	linux-nvdimm@lists.01.org, Matthew Wilcox <willy@infradead.org>,
	Jane Chu <jane.chu@oracle.com>,
	Muchun Song <songmuchun@bytedance.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH RFC 6/9] mm/gup: Grab head page refcount once for group of subpages
Date: Wed, 9 Dec 2020 11:05:39 +0000	[thread overview]
Message-ID: <b7f5fe44-f2f5-aea6-57b3-7e14a9ef624d@oracle.com> (raw)
In-Reply-To: <20201208194905.GQ5487@ziepe.ca>



On 12/8/20 7:49 PM, Jason Gunthorpe wrote:
> On Tue, Dec 08, 2020 at 05:28:58PM +0000, Joao Martins wrote:
>> Much like hugetlbfs or THPs, we treat device pagemaps with
>> compound pages like the rest of GUP handling of compound pages.
>>
>> Rather than incrementing the refcount every 4K, we record
>> all sub pages and increment by @refs amount *once*.
>>
>> Performance measured by gup_benchmark improves considerably
>> get_user_pages_fast() and pin_user_pages_fast():
>>
>>  $ gup_benchmark -f /dev/dax0.2 -m 16384 -r 10 -S [-u,-a] -n 512 -w
>>
>> (get_user_pages_fast 2M pages) ~75k us -> ~3.6k us
>> (pin_user_pages_fast 2M pages) ~125k us -> ~3.8k us
>>
>> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
>>  mm/gup.c | 67 ++++++++++++++++++++++++++++++++++++++++++--------------
>>  1 file changed, 51 insertions(+), 16 deletions(-)
>>
>> diff --git a/mm/gup.c b/mm/gup.c
>> index 98eb8e6d2609..194e6981eb03 100644
>> +++ b/mm/gup.c
>> @@ -2250,22 +2250,68 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
>>  }
>>  #endif /* CONFIG_ARCH_HAS_PTE_SPECIAL */
>>  
>> +
>> +static int record_subpages(struct page *page, unsigned long addr,
>> +			   unsigned long end, struct page **pages)
>> +{
>> +	int nr;
>> +
>> +	for (nr = 0; addr != end; addr += PAGE_SIZE)
>> +		pages[nr++] = page++;
>> +
>> +	return nr;
>> +}
>> +
>>  #if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
>> -static int __gup_device_huge(unsigned long pfn, unsigned long addr,
>> -			     unsigned long end, unsigned int flags,
>> -			     struct page **pages, int *nr)
>> +static int __gup_device_compound_huge(struct dev_pagemap *pgmap,
>> +				      struct page *head, unsigned long sz,
>> +				      unsigned long addr, unsigned long end,
>> +				      unsigned int flags, struct page **pages)
>> +{
>> +	struct page *page;
>> +	int refs;
>> +
>> +	if (!(pgmap->flags & PGMAP_COMPOUND))
>> +		return -1;
>> +
>> +	page = head + ((addr & (sz-1)) >> PAGE_SHIFT);
> 
> All the places that call record_subpages do some kind of maths like
> this, it should be placed inside record_subpages and not opencoded
> everywhere.
> 
Makes sense.

>> +	refs = record_subpages(page, addr, end, pages);
>> +
>> +	SetPageReferenced(page);
>> +	head = try_grab_compound_head(head, refs, flags);
>> +	if (!head) {
>> +		ClearPageReferenced(page);
>> +		return 0;
>> +	}
>> +
>> +	return refs;
>> +}
> 
> Why is all of this special? Any time we see a PMD/PGD/etc pointing to
> PFN we can apply this optimization. How come device has its own
> special path to do this?? 
> 
I think the reason is that zone_device struct pages have no relationship to one other. So
you anyways need to change individual pages, as opposed to just the head page.

I made it special to avoid breaking other ZONE_DEVICE users (and gating that with
PGMAP_COMPOUND). But if there's no concerns with that, I can unilaterally enable it.

> Why do we need to check PGMAP_COMPOUND? Why do we need to get pgmap?
> (We already removed that from the hmm version of this, was that wrong?
> Is this different?) Dan?
> 
> Also undo_dev_pagemap() is now out of date, we have unpin_user_pages()
> for that and no other error unwind touches ClearPageReferenced..
> 
/me nods Yeap I saw that too.

> Basic idea is good though!
> 
Cool, thanks!

	Joao


  reply	other threads:[~2020-12-09 11:06 UTC|newest]

Thread overview: 147+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-08 17:28 [PATCH RFC 0/9] mm, sparse-vmemmap: Introduce compound pagemaps Joao Martins
2020-12-08 17:28 ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 1/9] memremap: add ZONE_DEVICE support for compound pages Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-09  5:59   ` John Hubbard
2020-12-09  5:59     ` John Hubbard
2020-12-09  6:33     ` Matthew Wilcox
2020-12-09  6:33       ` Matthew Wilcox
2020-12-09 13:12       ` Joao Martins
2020-12-09 13:12         ` Joao Martins
2021-02-20  1:43     ` Dan Williams
2021-02-20  1:43       ` Dan Williams
2021-02-22 11:24       ` Joao Martins
2021-02-22 11:24         ` Joao Martins
2021-02-22 20:37         ` Dan Williams
2021-02-22 20:37           ` Dan Williams
2021-02-23 15:46           ` Joao Martins
2021-02-23 15:46             ` Joao Martins
2021-02-23 16:50             ` Dan Williams
2021-02-23 16:50               ` Dan Williams
2021-02-23 17:18               ` Joao Martins
2021-02-23 17:18                 ` Joao Martins
2021-02-23 18:18                 ` Dan Williams
2021-02-23 18:18                   ` Dan Williams
2021-03-10 18:12           ` Joao Martins
2021-03-10 18:12             ` Joao Martins
2021-03-12  5:54             ` Dan Williams
2021-03-12  5:54               ` Dan Williams
2021-02-20  1:24   ` Dan Williams
2021-02-20  1:24     ` Dan Williams
2021-02-22 11:09     ` Joao Martins
2021-02-22 11:09       ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 2/9] sparse-vmemmap: Consolidate arguments in vmemmap section populate Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-09  6:16   ` John Hubbard
2020-12-09  6:16     ` John Hubbard
2020-12-09 13:51     ` Joao Martins
2020-12-09 13:51       ` Joao Martins
2021-02-20  1:49   ` Dan Williams
2021-02-20  1:49     ` Dan Williams
2021-02-22 11:26     ` Joao Martins
2021-02-22 11:26       ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 3/9] sparse-vmemmap: Reuse vmemmap areas for a given mhp_params::align Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-08 17:38   ` Joao Martins
2020-12-08 17:38     ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 3/9] sparse-vmemmap: Reuse vmemmap areas for a given page size Joao Martins
2020-12-08 17:28   ` Joao Martins
2021-02-20  3:34   ` Dan Williams
2021-02-20  3:34     ` Dan Williams
2021-02-22 11:42     ` Joao Martins
2021-02-22 11:42       ` Joao Martins
2021-02-22 22:40       ` Dan Williams
2021-02-22 22:40         ` Dan Williams
2021-02-23 15:46         ` Joao Martins
2021-02-23 15:46           ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 4/9] mm/page_alloc: Reuse tail struct pages for compound pagemaps Joao Martins
2020-12-08 17:28   ` Joao Martins
2021-02-20  6:17   ` Dan Williams
2021-02-20  6:17     ` Dan Williams
2021-02-22 12:01     ` Joao Martins
2021-02-22 12:01       ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 5/9] device-dax: Compound pagemap support Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 6/9] mm/gup: Grab head page refcount once for group of subpages Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-08 19:49   ` Jason Gunthorpe
2020-12-09 11:05     ` Joao Martins [this message]
2020-12-09 11:05       ` Joao Martins
2020-12-09 15:15       ` Jason Gunthorpe
2020-12-09 16:02         ` Joao Martins
2020-12-09 16:02           ` Joao Martins
2020-12-09 16:24           ` Jason Gunthorpe
2020-12-09 17:27             ` Joao Martins
2020-12-09 17:27               ` Joao Martins
2020-12-09 18:14             ` Matthew Wilcox
2020-12-09 18:14               ` Matthew Wilcox
2020-12-09 19:08               ` Jason Gunthorpe
2020-12-10 15:43               ` Joao Martins
2020-12-10 15:43                 ` Joao Martins
2020-12-09  4:40   ` John Hubbard
2020-12-09  4:40     ` John Hubbard
2020-12-09 13:44     ` Joao Martins
2020-12-09 13:44       ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 7/9] mm/gup: Decrement head page " Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-08 19:34   ` Jason Gunthorpe
2020-12-09  5:06     ` John Hubbard
2020-12-09  5:06       ` John Hubbard
2020-12-09 13:43       ` Jason Gunthorpe
2020-12-09 12:17     ` Joao Martins
2020-12-09 12:17       ` Joao Martins
2020-12-17 19:05     ` Joao Martins
2020-12-17 19:05       ` Joao Martins
2020-12-17 20:05       ` Jason Gunthorpe
2020-12-17 22:34         ` Joao Martins
2020-12-17 22:34           ` Joao Martins
2020-12-18 14:25           ` Jason Gunthorpe
2020-12-19  2:06         ` John Hubbard
2020-12-19  2:06           ` John Hubbard
2020-12-19 13:10           ` Joao Martins
2020-12-19 13:10             ` Joao Martins
2020-12-08 17:29 ` [PATCH RFC 8/9] RDMA/umem: batch page unpin in __ib_mem_release() Joao Martins
2020-12-08 17:29   ` Joao Martins
2020-12-08 19:29   ` Jason Gunthorpe
2020-12-09 10:59     ` Joao Martins
2020-12-09 10:59       ` Joao Martins
2020-12-19 13:15       ` Joao Martins
2020-12-19 13:15         ` Joao Martins
2020-12-09  5:18   ` John Hubbard
2020-12-09  5:18     ` John Hubbard
2020-12-08 17:29 ` [PATCH RFC 9/9] mm: Add follow_devmap_page() for devdax vmas Joao Martins
2020-12-08 17:29   ` Joao Martins
2020-12-08 19:57   ` Jason Gunthorpe
2020-12-09  8:05     ` Christoph Hellwig
2020-12-09  8:05       ` Christoph Hellwig
2020-12-09 11:19     ` Joao Martins
2020-12-09 11:19       ` Joao Martins
2020-12-09  5:23   ` John Hubbard
2020-12-09  5:23     ` John Hubbard
2020-12-09  9:38 ` [PATCH RFC 0/9] mm, sparse-vmemmap: Introduce compound pagemaps David Hildenbrand
2020-12-09  9:38   ` David Hildenbrand
2020-12-09  9:52 ` [External] " Muchun Song
2020-12-09  9:52   ` Muchun Song
2021-02-20  1:18 ` Dan Williams
2021-02-20  1:18   ` Dan Williams
2021-02-22 11:06   ` Joao Martins
2021-02-22 11:06     ` Joao Martins
2021-02-22 14:32     ` Joao Martins
2021-02-22 14:32       ` Joao Martins
2021-02-23 16:28   ` Joao Martins
2021-02-23 16:28     ` Joao Martins
2021-02-23 16:44     ` Dan Williams
2021-02-23 16:44       ` Dan Williams
2021-02-23 17:15       ` Joao Martins
2021-02-23 17:15         ` Joao Martins
2021-02-23 18:15         ` Dan Williams
2021-02-23 18:15           ` Dan Williams
2021-02-23 18:54       ` Jason Gunthorpe
2021-02-23 22:48         ` Dan Williams
2021-02-23 22:48           ` Dan Williams
2021-02-23 23:07           ` Jason Gunthorpe
2021-02-24  0:14             ` Dan Williams
2021-02-24  0:14               ` Dan Williams
2021-02-24  1:00               ` Jason Gunthorpe
2021-02-24  1:32                 ` Dan Williams
2021-02-24  1:32                   ` Dan Williams

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