linux-kernel - Re: [PATCH 2/2] selftests/mm: Do not fail test for a single migration failure

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Message-ID: <e3bf3d2b-eb19-4678-916e-7a7f572b2936@linuxfoundation.org>
Date: Fri, 9 Aug 2024 11:13:02 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: Dev Jain <dev.jain@....com>, akpm@...ux-foundation.org, shuah@...nel.org,
 david@...hat.com, willy@...radead.org
Cc: ryan.roberts@....com, anshuman.khandual@....com, catalin.marinas@....com,
 cl@...two.org, vbabka@...e.cz, mhocko@...e.com, apopple@...dia.com,
 osalvador@...e.de, baolin.wang@...ux.alibaba.com,
 dave.hansen@...ux.intel.com, will@...nel.org, baohua@...nel.org,
 ioworker0@...il.com, gshan@...hat.com, mark.rutland@....com,
 kirill.shutemov@...ux.intel.com, hughd@...gle.com, aneesh.kumar@...nel.org,
 yang@...amperecomputing.com, peterx@...hat.com, broonie@...nel.org,
 mgorman@...hsingularity.net, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-kselftest@...r.kernel.org, Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH 2/2] selftests/mm: Do not fail test for a single migration
 failure

On 8/9/24 04:31, Dev Jain wrote:
> Do not fail the test for just a single instance of migration failure,
> since migration is a best-effort service.

The cover letter says:

"Given that migration is a best-effort service, it is wrong to fail the
test for just a single failure; hence, fail the test after 100 consecutive
failures (where 100 is still a subjective choice)."

You do want to mention the above here.

The reason being, I would like to know what this does to the run-time of
this test if migration fails and retried 100 times.

> 
> Signed-off-by: Dev Jain <dev.jain@....com>
> Suggested-by: David Hildenbrand <david@...hat.com>
> Reviewed-by: Ryan Roberts <ryan.roberts@....com>
> Tested-by: Ryan Roberts <ryan.roberts@....com>
> ---
>   tools/testing/selftests/mm/migration.c | 17 +++++++++++------
>   1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/migration.c b/tools/testing/selftests/mm/migration.c
> index 6908569ef406..64bcbb7151cf 100644
> --- a/tools/testing/selftests/mm/migration.c
> +++ b/tools/testing/selftests/mm/migration.c
> @@ -15,10 +15,10 @@
>   #include <signal.h>
>   #include <time.h>
>   
> -#define TWOMEG (2<<20)
> -#define RUNTIME (20)
> -
> -#define ALIGN(x, a) (((x) + (a - 1)) & (~((a) - 1)))
> +#define TWOMEG		(2<<20)
> +#define RUNTIME		(20)
> +#define MAX_RETRIES	100
> +#define ALIGN(x, a)	(((x) + (a - 1)) & (~((a) - 1)))
>   
>   FIXTURE(migration)
>   {
> @@ -65,6 +65,7 @@ int migrate(uint64_t *ptr, int n1, int n2)
>   	int ret, tmp;
>   	int status = 0;
>   	struct timespec ts1, ts2;
> +	int failures = 0;
>   
>   	if (clock_gettime(CLOCK_MONOTONIC, &ts1))
>   		return -1;
> @@ -79,13 +80,17 @@ int migrate(uint64_t *ptr, int n1, int n2)
>   		ret = move_pages(0, 1, (void **) &ptr, &n2, &status,
>   				MPOL_MF_MOVE_ALL);
>   		if (ret) {
> -			if (ret > 0)
> +			if (ret > 0) {
> +				/* Migration is best effort; try again */
> +				if (++failures < MAX_RETRIES)
> +					continue;
>   				printf("Didn't migrate %d pages\n", ret);
> +			}
>   			else
>   				perror("Couldn't migrate pages");
>   			return -2;
>   		}
> -
> +		failures = 0;
>   		tmp = n2;
>   		n2 = n1;
>   		n1 = tmp;

thanks,
-- Shuah