Re: [PATCH 2/3] mm/gup_benchmark: support pin_user_pages() and related calls

From: Nathan Chancellor
Date: Mon Jan 27 2020 - 15:52:56 EST

Hi John,

On Fri, Jan 24, 2020 at 06:11:14PM -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_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@xxxxxxxxx>
> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
> ---
> mm/gup_benchmark.c | 70 ++++++++++++++++++++--
> tools/testing/selftests/vm/gup_benchmark.c | 15 ++++-
> 2 files changed, 79 insertions(+), 6 deletions(-)
>
> diff --git a/mm/gup_benchmark.c b/mm/gup_benchmark.c
> index 8dba38e79a9f..3d5fb765e4e6 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 +21,47 @@ struct gup_benchmark {
> __u64 expansion[10]; /* For future use */
> };
>
> +static void put_back_pages(int cmd, struct page **pages, unsigned long nr_pages)

We received a Clang build report on this patch because the use of
PIN_FAST_BENCHMARK and PIN_BENCHMARK in the switch statement below will
overflow int; this should be unsigned int to match the cmd parameter in
the ioctls.

The report can be read here if you care for it:

https://groups.google.com/d/msg/clang-built-linux/gyGayC_dnis/D1celSStEgAJ

Cheers,
Nathan

> +{
> + int i;
> +
> + switch (cmd) {
> + case GUP_FAST_BENCHMARK:
> + case GUP_LONGTERM_BENCHMARK:
> + case GUP_BENCHMARK:
> + for (i = 0; i < nr_pages; i++)
> + put_page(pages[i]);
> + break;
> +
> + case PIN_FAST_BENCHMARK:
> + case PIN_BENCHMARK:
> + unpin_user_pages(pages, nr_pages);
> + break;
> + }
> +}
> +
> +static void verify_dma_pinned(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++) {
> + page = pages[i];
> + if (WARN(!page_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)
> {
> @@ -66,6 +109,14 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
> nr = get_user_pages(addr, nr, gup->flags, pages + i,
> NULL);
> break;
> + case PIN_FAST_BENCHMARK:
> + nr = pin_user_pages_fast(addr, nr, gup->flags,
> + pages + i);
> + break;
> + case PIN_BENCHMARK:
> + nr = pin_user_pages(addr, nr, gup->flags, pages + i,
> + NULL);
> + break;
> default:
> kvfree(pages);
> ret = -EINVAL;
> @@ -78,15 +129,22 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
> }
> end_time = ktime_get();
>
> + /* Shifting the meaning of nr_pages: now it is actual number pinned: */
> + nr_pages = i;
> +
> gup->get_delta_usec = ktime_us_delta(end_time, start_time);
> gup->size = addr - gup->addr;
>
> + /*
> + * Take an un-benchmark-timed moment to verify DMA pinned
> + * state: print a warning if any non-dma-pinned pages are found:
> + */
> + verify_dma_pinned(cmd, pages, nr_pages);
> +
> start_time = ktime_get();
> - for (i = 0; i < nr_pages; i++) {
> - if (!pages[i])
> - break;
> - put_page(pages[i]);
> - }
> +
> + put_back_pages(cmd, pages, nr_pages);
> +
> end_time = ktime_get();
> gup->put_delta_usec = ktime_us_delta(end_time, start_time);
>
> @@ -105,6 +163,8 @@ static long gup_benchmark_ioctl(struct file *filep, unsigned int cmd,
> case GUP_FAST_BENCHMARK:
> case GUP_LONGTERM_BENCHMARK:
> case GUP_BENCHMARK:
> + case PIN_FAST_BENCHMARK:
> + case PIN_BENCHMARK:
> break;
> default:
> return -EINVAL;
> diff --git a/tools/testing/selftests/vm/gup_benchmark.c b/tools/testing/selftests/vm/gup_benchmark.c
> index 389327e9b30a..43b4dfe161a2 100644
> --- a/tools/testing/selftests/vm/gup_benchmark.c
> +++ b/tools/testing/selftests/vm/gup_benchmark.c
> @@ -18,6 +18,10 @@
> #define GUP_LONGTERM_BENCHMARK _IOWR('g', 2, struct gup_benchmark)
> #define GUP_BENCHMARK _IOWR('g', 3, 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)
> +
> /* Just the flags we need, copied from mm.h: */
> #define FOLL_WRITE 0x01 /* check pte is writable */
>
> @@ -40,8 +44,14 @@ int main(int argc, char **argv)
> char *file = "/dev/zero";
> char *p;
>
> - while ((opt = getopt(argc, argv, "m:r:n:f:tTLUwSH")) != -1) {
> + while ((opt = getopt(argc, argv, "m:r:n:f:abtTLUuwSH")) != -1) {
> switch (opt) {
> + case 'a':
> + cmd = PIN_FAST_BENCHMARK;
> + break;
> + case 'b':
> + cmd = PIN_BENCHMARK;
> + break;
> case 'm':
> size = atoi(optarg) * MB;
> break;
> @@ -63,6 +73,9 @@ int main(int argc, char **argv)
> case 'U':
> cmd = GUP_BENCHMARK;
> break;
> + case 'u':
> + cmd = GUP_FAST_BENCHMARK;
> + break;
> case 'w':
> write = 1;
> break;
> --
> 2.25.0
>