linux-kernel - Re: [PATCH v4 20/23] mm/gup_benchmark: use proper FOLL

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Message-ID: <20191113190116.GA12947@iweiny-DESK2.sc.intel.com>
Date:   Wed, 13 Nov 2019 11:01:17 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Alex Williamson <alex.williamson@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Chinner <david@...morbit.com>,
        David Airlie <airlied@...ux.ie>,
        "David S . Miller" <davem@...emloft.net>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>,
        Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Paul Mackerras <paulus@...ba.org>,
        Shuah Khan <shuah@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>, bpf@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, kvm@...r.kernel.org,
        linux-block@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-media@...r.kernel.org, linux-rdma@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, netdev@...r.kernel.org,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 20/23] mm/gup_benchmark: use proper FOLL_WRITE flags
 instead of hard-coding "1"

On Tue, Nov 12, 2019 at 08:27:07PM -0800, John Hubbard wrote:
> Fix the gup benchmark flags to use the symbolic FOLL_WRITE,
> instead of a hard-coded "1" value.
> 
> Also, clean up the filtering of gup flags a little, by just doing
> it once before issuing any of the get_user_pages*() calls. This
> makes it harder to overlook, instead of having little "gup_flags & 1"
> phrases in the function calls.
> 
> Signed-off-by: John Hubbard <jhubbard@...dia.com>

Reviewed-by: Ira Weiny <ira.weiny@...el.com>

> ---
>  mm/gup_benchmark.c                         | 9 ++++++---
>  tools/testing/selftests/vm/gup_benchmark.c | 6 +++++-
>  2 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/gup_benchmark.c b/mm/gup_benchmark.c
> index 7dd602d7f8db..7fc44d25eca7 100644
> --- a/mm/gup_benchmark.c
> +++ b/mm/gup_benchmark.c
> @@ -48,18 +48,21 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
>  			nr = (next - addr) / PAGE_SIZE;
>  		}
>  
> +		/* Filter out most gup flags: only allow a tiny subset here: */
> +		gup->flags &= FOLL_WRITE;
> +
>  		switch (cmd) {
>  		case GUP_FAST_BENCHMARK:
> -			nr = get_user_pages_fast(addr, nr, gup->flags & 1,
> +			nr = get_user_pages_fast(addr, nr, gup->flags,
>  						 pages + i);
>  			break;
>  		case GUP_LONGTERM_BENCHMARK:
>  			nr = get_user_pages(addr, nr,
> -					    (gup->flags & 1) | FOLL_LONGTERM,
> +					    gup->flags | FOLL_LONGTERM,
>  					    pages + i, NULL);
>  			break;
>  		case GUP_BENCHMARK:
> -			nr = get_user_pages(addr, nr, gup->flags & 1, pages + i,
> +			nr = get_user_pages(addr, nr, gup->flags, pages + i,
>  					    NULL);
>  			break;
>  		default:
> diff --git a/tools/testing/selftests/vm/gup_benchmark.c b/tools/testing/selftests/vm/gup_benchmark.c
> index 485cf06ef013..389327e9b30a 100644
> --- a/tools/testing/selftests/vm/gup_benchmark.c
> +++ b/tools/testing/selftests/vm/gup_benchmark.c
> @@ -18,6 +18,9 @@
>  #define GUP_LONGTERM_BENCHMARK	_IOWR('g', 2, struct gup_benchmark)
>  #define GUP_BENCHMARK		_IOWR('g', 3, struct gup_benchmark)
>  
> +/* Just the flags we need, copied from mm.h: */
> +#define FOLL_WRITE	0x01	/* check pte is writable */
> +
>  struct gup_benchmark {
>  	__u64 get_delta_usec;
>  	__u64 put_delta_usec;
> @@ -85,7 +88,8 @@ int main(int argc, char **argv)
>  	}
>  
>  	gup.nr_pages_per_call = nr_pages;
> -	gup.flags = write;
> +	if (write)
> +		gup.flags |= FOLL_WRITE;
>  
>  	fd = open("/sys/kernel/debug/gup_benchmark", O_RDWR);
>  	if (fd == -1)
> -- 
> 2.24.0
>