Re: [PATCH] mm/gup_benchmark: use pin_user_pages for FOLL_LONGTERM flag

[John Hubbard <jhubbard@nvidia.com>]

On 8/15/20 5:20 AM, Barry Song wrote:
> According to Documentation/core-api/pin_user_pages.rst, FOLL_PIN is a
> prerequisite to FOLL_LONGTERM. Another way of saying that is,
> FOLL_LONGTERM is a specific case, more restrictive case of FOLL_PIN.
> 
> Almost all kernel modules are using pin_user_pages() with FOLL_LONGTERM,
> mm/gup_benchmark.c seems to the only exception in which FOLL_PIN is not
> a prerequisite to FOLL_LONGTERM.
> 
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Jérôme Glisse <jglisse@redhat.com>
> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Dave Chinner <david@fromorbit.com>
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
> ---
>   mm/gup_benchmark.c                         | 23 +++++++++++-----------
>   tools/testing/selftests/vm/gup_benchmark.c | 14 ++++++-------
>   2 files changed, 19 insertions(+), 18 deletions(-)
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Reviewed-by: John Hubbard <jhubbard@nvidia.com>

thanks,
-- 
John Hubbard
NVIDIA

> 
> diff --git a/mm/gup_benchmark.c b/mm/gup_benchmark.c
> index be690fa66a46..464cae1fa3ea 100644
> --- a/mm/gup_benchmark.c
> +++ b/mm/gup_benchmark.c
> @@ -6,10 +6,10 @@
>   #include <linux/debugfs.h>
>   
>   #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)
> +#define GUP_BENCHMARK		_IOWR('g', 2, struct gup_benchmark)
> +#define PIN_FAST_BENCHMARK	_IOWR('g', 3, struct gup_benchmark)
> +#define PIN_BENCHMARK		_IOWR('g', 4, struct gup_benchmark)
> +#define PIN_LONGTERM_BENCHMARK	_IOWR('g', 5, struct gup_benchmark)
>   
>   struct gup_benchmark {
>   	__u64 get_delta_usec;
> @@ -28,7 +28,6 @@ static void put_back_pages(unsigned int cmd, struct page **pages,
>   
>   	switch (cmd) {
>   	case GUP_FAST_BENCHMARK:
> -	case GUP_LONGTERM_BENCHMARK:
>   	case GUP_BENCHMARK:
>   		for (i = 0; i < nr_pages; i++)
>   			put_page(pages[i]);
> @@ -36,6 +35,7 @@ static void put_back_pages(unsigned int cmd, struct page **pages,
>   
>   	case PIN_FAST_BENCHMARK:
>   	case PIN_BENCHMARK:
> +	case PIN_LONGTERM_BENCHMARK:
>   		unpin_user_pages(pages, nr_pages);
>   		break;
>   	}
> @@ -50,6 +50,7 @@ static void verify_dma_pinned(unsigned int cmd, struct page **pages,
>   	switch (cmd) {
>   	case PIN_FAST_BENCHMARK:
>   	case PIN_BENCHMARK:
> +	case PIN_LONGTERM_BENCHMARK:
>   		for (i = 0; i < nr_pages; i++) {
>   			page = pages[i];
>   			if (WARN(!page_maybe_dma_pinned(page),
> @@ -101,11 +102,6 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
>   			nr = get_user_pages_fast(addr, nr, gup->flags,
>   						 pages + i);
>   			break;
> -		case GUP_LONGTERM_BENCHMARK:
> -			nr = get_user_pages(addr, nr,
> -					    gup->flags | FOLL_LONGTERM,
> -					    pages + i, NULL);
> -			break;
>   		case GUP_BENCHMARK:
>   			nr = get_user_pages(addr, nr, gup->flags, pages + i,
>   					    NULL);
> @@ -118,6 +114,11 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
>   			nr = pin_user_pages(addr, nr, gup->flags, pages + i,
>   					    NULL);
>   			break;
> +		case PIN_LONGTERM_BENCHMARK:
> +			nr = pin_user_pages(addr, nr,
> +					    gup->flags | FOLL_LONGTERM,
> +					    pages + i, NULL);
> +			break;
>   		default:
>   			kvfree(pages);
>   			ret = -EINVAL;
> @@ -162,10 +163,10 @@ static long gup_benchmark_ioctl(struct file *filep, unsigned int cmd,
>   
>   	switch (cmd) {
>   	case GUP_FAST_BENCHMARK:
> -	case GUP_LONGTERM_BENCHMARK:
>   	case GUP_BENCHMARK:
>   	case PIN_FAST_BENCHMARK:
>   	case PIN_BENCHMARK:
> +	case PIN_LONGTERM_BENCHMARK:
>   		break;
>   	default:
>   		return -EINVAL;
> diff --git a/tools/testing/selftests/vm/gup_benchmark.c b/tools/testing/selftests/vm/gup_benchmark.c
> index 43b4dfe161a2..31f8bb086907 100644
> --- a/tools/testing/selftests/vm/gup_benchmark.c
> +++ b/tools/testing/selftests/vm/gup_benchmark.c
> @@ -15,12 +15,12 @@
>   #define PAGE_SIZE sysconf(_SC_PAGESIZE)
>   
>   #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 GUP_BENCHMARK		_IOWR('g', 2, struct gup_benchmark)
>   
>   /* Similar to above, but use FOLL_PIN instead of FOLL_GET. */
> -#define PIN_FAST_BENCHMARK	_IOWR('g', 4, struct gup_benchmark)
> -#define PIN_BENCHMARK		_IOWR('g', 5, struct gup_benchmark)
> +#define PIN_FAST_BENCHMARK	_IOWR('g', 3, struct gup_benchmark)
> +#define PIN_BENCHMARK		_IOWR('g', 4, struct gup_benchmark)
> +#define PIN_LONGTERM_BENCHMARK	_IOWR('g', 5, struct gup_benchmark)
>   
>   /* Just the flags we need, copied from mm.h: */
>   #define FOLL_WRITE	0x01	/* check pte is writable */
> @@ -52,6 +52,9 @@ int main(int argc, char **argv)
>   		case 'b':
>   			cmd = PIN_BENCHMARK;
>   			break;
> +		case 'L':
> +			cmd = PIN_LONGTERM_BENCHMARK;
> +			break;
>   		case 'm':
>   			size = atoi(optarg) * MB;
>   			break;
> @@ -67,9 +70,6 @@ int main(int argc, char **argv)
>   		case 'T':
>   			thp = 0;
>   			break;
> -		case 'L':
> -			cmd = GUP_LONGTERM_BENCHMARK;
> -			break;
>   		case 'U':
>   			cmd = GUP_BENCHMARK;
>   			break;
>