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 9/9] mm: Add follow_devmap_page() for devdax vmas
Date: Wed, 9 Dec 2020 11:19:04 +0000 [thread overview]
Message-ID: <7cf4de6b-5377-394b-d95a-586e6422b9cd@oracle.com> (raw)
In-Reply-To: <20201208195754.GR5487@ziepe.ca>
On 12/8/20 7:57 PM, Jason Gunthorpe wrote:
> On Tue, Dec 08, 2020 at 05:29:01PM +0000, Joao Martins wrote:
>> Similar to follow_hugetlb_page() add a follow_devmap_page which rather
>> than calling follow_page() per 4K page in a PMD/PUD it does so for the
>> entire PMD, where we lock the pmd/pud, get all pages , unlock.
>>
>> While doing so, we only change the refcount once when PGMAP_COMPOUND is
>> passed in.
>>
>> This let us improve {pin,get}_user_pages{,_longterm}() considerably:
>>
>> $ gup_benchmark -f /dev/dax0.2 -m 16384 -r 10 -S [-U,-b,-L] -n 512 -w
>>
>> (<test>) [before] -> [after]
>> (get_user_pages 2M pages) ~150k us -> ~8.9k us
>> (pin_user_pages 2M pages) ~192k us -> ~9k us
>> (pin_user_pages_longterm 2M pages) ~200k us -> ~19k us
>>
>> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
>> ---
>> I've special-cased this to device-dax vmas given its similar page size
>> guarantees as hugetlbfs, but I feel this is a bit wrong. I am
>> replicating follow_hugetlb_page() as RFC ought to seek feedback whether
>> this should be generalized if no fundamental issues exist. In such case,
>> should I be changing follow_page_mask() to take either an array of pages
>> or a function pointer and opaque arguments which would let caller pick
>> its structure?
>
> I would be extremely sad if this was the only way to do this :(
>
> We should be trying to make things more general.
Yeap, indeed.
Specially, when similar problem is observed for THP, at least from the
measurements I saw. It is all slow, except for hugetlbfs.
> The
> hmm_range_fault_path() doesn't have major special cases for device, I
> am struggling to understand why gup fast and slow do.
>
> What we've talked about is changing the calling convention across all
> of this to something like:
>
> struct gup_output {
> struct page **cur;
> struct page **end;
> unsigned long vaddr;
> [..]
> }
>
> And making the manipulator like you saw for GUP common:
>
> gup_output_single_page()
> gup_output_pages()
>
> Then putting this eveywhere. This is the pattern that we ended up with
> in hmm_range_fault, and it seems to be working quite well.
>
> fast/slow should be much more symmetric in code than they are today,
> IMHO..
Thanks for the suggestions above.
I think those differences mainly exist because it used to be
> siloed in arch code. Some of the differences might be bugs, we've seen
> that a few times at least..
Interesting, wasn't aware of the siloing.
I'll go investigate how this all refactoring goes together, at the point
of which a future iteration of this particular patch probably needs to
move independently from this series.
Joao
next prev parent reply other threads:[~2020-12-09 11:21 UTC|newest]
Thread overview: 80+ 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 ` [PATCH RFC 1/9] memremap: add ZONE_DEVICE support for compound pages Joao Martins
2020-12-09 5:59 ` John Hubbard
2020-12-09 6:33 ` Matthew Wilcox
2020-12-09 13:12 ` Joao Martins
2021-02-20 1:43 ` Dan Williams
2021-02-22 11:24 ` Joao Martins
2021-02-22 20:37 ` Dan Williams
2021-02-23 15:46 ` Joao Martins
2021-02-23 16:50 ` Dan Williams
2021-02-23 17:18 ` Joao Martins
2021-02-23 18:18 ` Dan Williams
2021-03-10 18:12 ` Joao Martins
2021-03-12 5:54 ` Dan Williams
2021-02-20 1:24 ` Dan Williams
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
2020-12-09 6:16 ` John Hubbard
2020-12-09 13:51 ` Joao Martins
2021-02-20 1:49 ` Dan Williams
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 17:38 ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 3/9] sparse-vmemmap: Reuse vmemmap areas for a given page size Joao Martins
2021-02-20 3:34 ` Dan Williams
2021-02-22 11:42 ` Joao Martins
2021-02-22 22:40 ` Dan Williams
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
2021-02-20 6:17 ` Dan Williams
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 ` [PATCH RFC 6/9] mm/gup: Grab head page refcount once for group of subpages Joao Martins
2020-12-08 19:49 ` Jason Gunthorpe
2020-12-09 11:05 ` Joao Martins
2020-12-09 15:15 ` Jason Gunthorpe
2020-12-09 16:02 ` Joao Martins
2020-12-09 16:24 ` Jason Gunthorpe
2020-12-09 17:27 ` Joao Martins
2020-12-09 18:14 ` Matthew Wilcox
2020-12-09 19:08 ` Jason Gunthorpe
2020-12-10 15:43 ` Joao Martins
2020-12-09 4:40 ` John Hubbard
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 19:34 ` Jason Gunthorpe
2020-12-09 5:06 ` John Hubbard
2020-12-09 13:43 ` Jason Gunthorpe
2020-12-09 12:17 ` Joao Martins
2020-12-17 19:05 ` Joao Martins
2020-12-17 20:05 ` Jason Gunthorpe
2020-12-17 22:34 ` Joao Martins
2020-12-18 14:25 ` Jason Gunthorpe
2020-12-19 2:06 ` John Hubbard
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 19:29 ` Jason Gunthorpe
2020-12-09 10:59 ` Joao Martins
2020-12-19 13:15 ` Joao Martins
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 19:57 ` Jason Gunthorpe
2020-12-09 8:05 ` Christoph Hellwig
2020-12-09 11:19 ` Joao Martins [this message]
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 9:52 ` [External] " Muchun Song
2021-02-20 1:18 ` Dan Williams
2021-02-22 11:06 ` Joao Martins
2021-02-22 14:32 ` Joao Martins
2021-02-23 16:28 ` Joao Martins
2021-02-23 16:44 ` Dan Williams
2021-02-23 17:15 ` Joao Martins
2021-02-23 18:15 ` Dan Williams
2021-02-23 18:54 ` Jason Gunthorpe
2021-02-23 22:48 ` Dan Williams
2021-02-23 23:07 ` Jason Gunthorpe
2021-02-24 0:14 ` Dan Williams
2021-02-24 1:00 ` Jason Gunthorpe
2021-02-24 1:32 ` Dan Williams
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