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Date:   Wed, 5 Feb 2020 10:37:33 +0100
From:   Jan Kara <jack@suse.cz>
To:     John Hubbard <jhubbard@nvidia.com>
Cc:     Andrew Morton <akpm@linux-foundation.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>,
        Ira Weiny <ira.weiny@intel.com>, Jan Kara <jack@suse.cz>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Jonathan Corbet <corbet@lwn.net>,
        =?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Michal Hocko <mhocko@suse.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Shuah Khan <shuah@kernel.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Matthew Wilcox <willy@infradead.org>,
        linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kselftest@vger.kernel.org, linux-rdma@vger.kernel.org,
        linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 10/12] mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN)
 reporting
Message-ID: <20200205093733.GB28058@quack2.suse.cz>
References: <20200204234117.2974687-1-jhubbard@nvidia.com>
 <20200204234117.2974687-11-jhubbard@nvidia.com>
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On Tue 04-02-20 15:41:15, John Hubbard wrote:
> Now that pages are "DMA-pinned" via pin_user_page*(), and unpinned via
> unpin_user_pages*(), we need some visibility into whether all of this is
> working correctly.
> 
> Add two new fields to /proc/vmstat:
> 
>     nr_foll_pin_acquired
>     nr_foll_pin_released
> 
> These are documented in Documentation/core-api/pin_user_pages.rst.
> They represent the number of pages (since boot time) that have been
> pinned ("nr_foll_pin_acquired") and unpinned ("nr_foll_pin_released"),
> via pin_user_pages*() and unpin_user_pages*().
> 
> In the absence of long-running DMA or RDMA operations that hold pages
> pinned, the above two fields will normally be equal to each other.
> 
> Also: update Documentation/core-api/pin_user_pages.rst, to remove an
> earlier (now confirmed untrue) claim about a performance problem with
> /proc/vmstat.
> 
> Also: updated Documentation/core-api/pin_user_pages.rst to rename the
> new /proc/vmstat entries, to the names listed here.
> 
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

...

> @@ -104,6 +106,9 @@ static __maybe_unused struct page *try_grab_compound_head(struct page *page,
>  		if (hpage_pincount_available(page))
>  			hpage_pincount_add(page, refs);
>  
> +		mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED,
> +				    orig_refs);
> +
>  		return page;
>  	}
>  

It seems to me you miss mod_node_page_state() in put_compound_head(), don't
you?

Otherwise I like the new stat names better :).

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