Re: [PATCH v3 6/7] selftest/mm: ksm_functional_tests: test in mmap_and_merge_range() if anything got merged

From: Peter Xu <peterx@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org, kvm@vger.kernel.org,
	linux-kselftest@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	liubo <liubo254@huawei.com>, Matthew Wilcox <willy@infradead.org>,
	Hugh Dickins <hughd@google.com>, Jason Gunthorpe <jgg@ziepe.ca>,
	John Hubbard <jhubbard@nvidia.com>, Mel Gorman <mgorman@suse.de>,
	Shuah Khan <shuah@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH v3 6/7] selftest/mm: ksm_functional_tests: test in mmap_and_merge_range() if anything got merged
Date: Thu, 3 Aug 2023 15:05:21 -0400	[thread overview]
Message-ID: <ZMv6cZH2PdyeTmw1@x1n> (raw)
In-Reply-To: <20230803143208.383663-7-david@redhat.com>

On Thu, Aug 03, 2023 at 04:32:07PM +0200, David Hildenbrand wrote:
> Let's extend mmap_and_merge_range() to test if anything in the current
> process was merged. range_maps_duplicates() is too unreliable for that
> use case, so instead look at KSM stats.
> 
> Trigger a complete unmerge first, to cleanup the stable tree and
> stabilize accounting of merged pages.
> 
> Note that we're using /proc/self/ksm_merging_pages instead of
> /proc/self/ksm_stat, because that one is available in more existing
> kernels.
> 
> If /proc/self/ksm_merging_pages can't be opened, we can't perform any
> checks and simply skip them.
> 
> We have to special-case the shared zeropage for now. But the only user
> -- test_unmerge_zero_pages() -- performs its own merge checks.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>

Acked-by: Peter Xu <peterx@redhat.com>

One nitpick:

> ---
>  .../selftests/mm/ksm_functional_tests.c       | 47 +++++++++++++++++++
>  1 file changed, 47 insertions(+)
> 
> diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
> index 0de9d33cd565..cb63b600cb4f 100644
> --- a/tools/testing/selftests/mm/ksm_functional_tests.c
> +++ b/tools/testing/selftests/mm/ksm_functional_tests.c
> @@ -30,6 +30,7 @@
>  static int ksm_fd;
>  static int ksm_full_scans_fd;
>  static int proc_self_ksm_stat_fd;
> +static int proc_self_ksm_merging_pages_fd;
>  static int ksm_use_zero_pages_fd;
>  static int pagemap_fd;
>  static size_t pagesize;
> @@ -88,6 +89,22 @@ static long get_my_ksm_zero_pages(void)
>  	return my_ksm_zero_pages;
>  }
>  
> +static long get_my_merging_pages(void)
> +{
> +	char buf[10];
> +	ssize_t ret;
> +
> +	if (proc_self_ksm_merging_pages_fd < 0)
> +		return proc_self_ksm_merging_pages_fd;

Better do the fds check all in main(), e.g. not all callers below considers
negative values, so -1 can pass "if (get_my_merging_pages())" etc.

> +
> +	ret = pread(proc_self_ksm_merging_pages_fd, buf, sizeof(buf) - 1, 0);
> +	if (ret <= 0)
> +		return -errno;
> +	buf[ret] = 0;
> +
> +	return strtol(buf, NULL, 10);
> +}

-- 
Peter Xu