From: Ira Weiny <ira.weiny@intel.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: John Hubbard <jhubbard@nvidia.com>,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@suse.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Jason Gunthorpe <jgg@ziepe.ca>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
"David S. Miller" <davem@davemloft.net>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
Rich Felker <dalias@libc.org>,
Yoshinori Sato <ysato@users.sourceforge.jp>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Ralf Baechle <ralf@linux-mips.org>,
Paul Burton <paul.burton@mips.com>,
James Hogan <jhogan@kernel.org>,
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Subject: Re: [RESEND PATCH 0/7] Add FOLL_LONGTERM to GUP fast and use it
Date: Wed, 20 Feb 2019 10:02:56 -0800 [thread overview]
Message-ID: <20190220180255.GA12020@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <20190220151930.GB11695@infradead.org>
On Wed, Feb 20, 2019 at 07:19:30AM -0800, Christoph Hellwig wrote:
> On Tue, Feb 19, 2019 at 09:30:33PM -0800, ira.weiny@intel.com wrote:
> > From: Ira Weiny <ira.weiny@intel.com>
> >
> > Resending these as I had only 1 minor comment which I believe we have covered
> > in this series. I was anticipating these going through the mm tree as they
> > depend on a cleanup patch there and the IB changes are very minor. But they
> > could just as well go through the IB tree.
> >
> > NOTE: This series depends on my clean up patch to remove the write parameter
> > from gup_fast_permitted()[1]
> >
> > HFI1, qib, and mthca, use get_user_pages_fast() due to it performance
> > advantages. These pages can be held for a significant time. But
> > get_user_pages_fast() does not protect against mapping of FS DAX pages.
>
> This I don't get - if you do lock down long term mappings performance
> of the actual get_user_pages call shouldn't matter to start with.
>
> What do I miss?
A couple of points.
First "longterm" is a relative thing and at this point is probably a misnomer.
This is really flagging a pin which is going to be given to hardware and can't
move. I've thought of a couple of alternative names but I think we have to
settle on if we are going to use FL_LAYOUT or something else to solve the
"longterm" problem. Then I think we can change the flag to a better name.
Second, It depends on how often you are registering memory. I have spoken with
some RDMA users who consider MR in the performance path... For the overall
application performance. I don't have the numbers as the tests for HFI1 were
done a long time ago. But there was a significant advantage. Some of which is
probably due to the fact that you don't have to hold mmap_sem.
Finally, architecturally I think it would be good for everyone to use *_fast.
There are patches submitted to the RDMA list which would allow the use of
*_fast (they reworking the use of mmap_sem) and as soon as they are accepted
I'll submit a patch to convert the RDMA core as well. Also to this point
others are looking to use *_fast.[2]
As an asside, Jasons pointed out in my previous submission that *_fast and
*_unlocked look very much the same. I agree and I think further cleanup will
be coming. But I'm focused on getting the final solution for DAX at the
moment.
Ira
next prev parent reply other threads:[~2019-02-20 18:03 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-20 5:30 [RESEND PATCH 0/7] Add FOLL_LONGTERM to GUP fast and use it ira.weiny
2019-02-20 5:30 ` [RESEND PATCH 1/7] mm/gup: Replace get_user_pages_longterm() with FOLL_LONGTERM ira.weiny
2019-02-20 5:30 ` [RESEND PATCH 2/7] mm/gup: Change write parameter to flags in fast walk ira.weiny
2019-02-20 5:30 ` [RESEND PATCH 3/7] mm/gup: Change GUP fast to use flags rather than a write 'bool' ira.weiny
2019-02-20 19:29 ` Mike Marshall
2019-02-21 3:18 ` Souptick Joarder
2019-02-21 22:24 ` Ira Weiny
2019-02-20 5:30 ` [RESEND PATCH 4/7] mm/gup: Add FOLL_LONGTERM capability to GUP fast ira.weiny
2019-02-20 5:30 ` [RESEND PATCH 5/7] IB/hfi1: Use the new FOLL_LONGTERM flag to get_user_pages_fast() ira.weiny
2019-02-20 5:30 ` [RESEND PATCH 6/7] IB/qib: " ira.weiny
2019-02-20 5:30 ` [RESEND PATCH 7/7] IB/mthca: " ira.weiny
2019-02-20 15:19 ` [RESEND PATCH 0/7] Add FOLL_LONGTERM to GUP fast and use it Christoph Hellwig
2019-02-20 18:02 ` Ira Weiny [this message]
2019-02-27 19:14 ` Ira Weiny
2019-03-17 18:34 ira.weiny
2019-03-19 22:19 ` Andrew Morton
2019-03-21 8:40 ` Ira Weiny
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