linux-kernel - Re: [PATCH v3 6/7] selftest/mm: ksm_functional_tests: test in mmap_and_merge

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Date:   Thu, 3 Aug 2023 15:05:21 -0400
From:   Peter Xu <peterx@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        liubo <liubo254@...wei.com>,
        Matthew Wilcox <willy@...radead.org>,
        Hugh Dickins <hughd@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        John Hubbard <jhubbard@...dia.com>,
        Mel Gorman <mgorman@...e.de>, Shuah Khan <shuah@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v3 6/7] selftest/mm: ksm_functional_tests: test in
 mmap_and_merge_range() if anything got merged

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@...hat.com>

Acked-by: Peter Xu <peterx@...hat.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