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Date:   Wed, 18 Nov 2020 14:49:52 +0100
From:   Jan Kara <jack@suse.cz>
To:     John Hubbard <jhubbard@nvidia.com>
Cc:     kernel test robot <oliver.sang@intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Jan Kara <jack@suse.cz>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Ira Weiny <ira.weiny@intel.com>,
        =?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Chinner <david@fromorbit.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Jonathan Corbet <corbet@lwn.net>,
        Michal Hocko <mhocko@suse.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
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Subject: Re: [mm/gup] 47e29d32af: phoronix-test-suite.npb.FT.A.total_mop_s
 -45.0% regression
Message-ID: <20201118134952.GE1981@quack2.suse.cz>
References: <20201117024825.GA8169@xsang-OptiPlex-9020>
 <24d9d093-5b7a-9aee-8d61-59c0007a9269@nvidia.com>
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On Mon 16-11-20 19:35:31, John Hubbard wrote:
> 
> On 11/16/20 6:48 PM, kernel test robot wrote:
> > 
> > Greeting,
> > 
> > FYI, we noticed a -45.0% regression of phoronix-test-suite.npb.FT.A.total_mop_s due to commit:
> > 
> 
> That's a huge slowdown...
> 
> > 
> > commit: 47e29d32afba11b13efb51f03154a8cf22fb4360 ("mm/gup: page->hpage_pinned_refcount: exact pin counts for huge pages")
> > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> 
> ...but that commit happened in April, 2020. Surely if this were a serious
> issue we would have some other indication...is this worth following up
> on?? I'm inclined to ignore it, honestly.

Why this was detected so late is a fair question although it doesn't quite
invalidate the report... The NPB benchmark appears to be a supercomputing
benchmark so concievably it could be heavily using THPs. The question is
why it would be a heavy user of pinning as well but even that is imaginable
considering that MPI is in use etc.

So maybe it is worth trying to reproduce this because heavy THP + pinning
users might be indeed rare and only those would show regressions in THP
pinning performance...

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR