linux-kernel - Re: [PATCH v3 11/12] mm/gup_benchmark: support pin_user

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Date:   Mon, 3 Feb 2020 16:58:45 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Shuah Khan <shuah@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 11/12] mm/gup_benchmark: support pin_user_pages() and
 related calls

On Fri, Jan 31, 2020 at 07:40:28PM -0800, John Hubbard wrote:
> Up until now, gup_benchmark supported testing of the
> following kernel functions:
> 
> * get_user_pages(): via the '-U' command line option
> * get_user_pages_longterm(): via the '-L' command line option
> * get_user_pages_fast(): as the default (no options required)
> 
> Add test coverage for the new corresponding pin_*() functions:
> 
> * pin_user_pages_fast(): via the '-a' command line option
> * pin_user_pages():      via the '-b' command line option
> 
> Also, add an option for clarity: '-u' for what is now (still) the
> default choice: get_user_pages_fast().
> 
> Also, for the commands that set FOLL_PIN, verify that the pages
> really are dma-pinned, via the new is_dma_pinned() routine.
> Those commands are:
> 
>     PIN_FAST_BENCHMARK     : calls pin_user_pages_fast()
>     PIN_BENCHMARK          : calls pin_user_pages()
> 
> In between the calls to pin_*() and unpin_user_pages(),
> check each page: if page_maybe_dma_pinned() returns false, then
> WARN and return.
> 
> Do this outside of the benchmark timestamps, so that it doesn't
> affect reported times.
> 
> Reviewed-by: Ira Weiny <ira.weiny@...el.com>
> Signed-off-by: John Hubbard <jhubbard@...dia.com>
> ---
>  mm/gup_benchmark.c                         | 71 ++++++++++++++++++++--
>  tools/testing/selftests/vm/gup_benchmark.c | 15 ++++-
>  2 files changed, 80 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/gup_benchmark.c b/mm/gup_benchmark.c
> index 8dba38e79a9f..447628d0131f 100644
> --- a/mm/gup_benchmark.c
> +++ b/mm/gup_benchmark.c
> @@ -8,6 +8,8 @@
>  #define GUP_FAST_BENCHMARK	_IOWR('g', 1, struct gup_benchmark)
>  #define GUP_LONGTERM_BENCHMARK	_IOWR('g', 2, struct gup_benchmark)
>  #define GUP_BENCHMARK		_IOWR('g', 3, struct gup_benchmark)
> +#define PIN_FAST_BENCHMARK	_IOWR('g', 4, struct gup_benchmark)
> +#define PIN_BENCHMARK		_IOWR('g', 5, struct gup_benchmark)
>  
>  struct gup_benchmark {
>  	__u64 get_delta_usec;
> @@ -19,6 +21,48 @@ struct gup_benchmark {
>  	__u64 expansion[10];	/* For future use */
>  };
>  
> +static void put_back_pages(unsigned int cmd, struct page **pages,
> +			   unsigned long nr_pages)
> +{
> +	int i;
> +
> +	switch (cmd) {
> +	case GUP_FAST_BENCHMARK:
> +	case GUP_LONGTERM_BENCHMARK:
> +	case GUP_BENCHMARK:
> +		for (i = 0; i < nr_pages; i++)

'i' is 'int' and 'nr_pages' is 'unsigned long'.
There's space for trouble :P

> +			put_page(pages[i]);
> +		break;
> +
> +	case PIN_FAST_BENCHMARK:
> +	case PIN_BENCHMARK:
> +		unpin_user_pages(pages, nr_pages);
> +		break;
> +	}
> +}
> +
> +static void verify_dma_pinned(unsigned int cmd, struct page **pages,
> +			      unsigned long nr_pages)
> +{
> +	int i;
> +	struct page *page;
> +
> +	switch (cmd) {
> +	case PIN_FAST_BENCHMARK:
> +	case PIN_BENCHMARK:
> +		for (i = 0; i < nr_pages; i++) {

Ditto.

> +			page = pages[i];
> +			if (WARN(!page_maybe_dma_pinned(page),
> +				 "pages[%d] is NOT dma-pinned\n", i)) {
> +
> +				dump_page(page, "gup_benchmark failure");
> +				break;
> +			}
> +		}
> +		break;
> +	}
> +}
> +
>  static int __gup_benchmark_ioctl(unsigned int cmd,
>  		struct gup_benchmark *gup)
>  {

-- 
 Kirill A. Shutemov