selftests/vm: add KSM unmerge tests

Patch series "mm/ksm: break_ksm() cleanups and fixes", v2.

This series cleans up and fixes break_ksm().  In summary, we no longer use
fake write faults to break COW but instead FAULT_FLAG_UNSHARE.  Further,
we move away from using follow_page() --- that we can hopefully remove
completely at one point --- and use new walk_page_range_vma() instead.

Fortunately, we can get rid of VM_FAULT_WRITE and FOLL_MIGRATION in common
code now.

Extend the existing ksm tests by an unmerge benchmark, and a some new
unmerge tests.

Also, add a selftest to measure MADV_UNMERGEABLE performance.  In my setup
(AMD Ryzen 9 3900X), running the KSM selftest to test unmerge performance
on 2 GiB (taskset 0x8 ./ksm_tests -D -s 2048), this results in a
performance degradation of ~6% -- 7% (old: ~5250 MiB/s, new: ~4900 MiB/s).
I don't think we particularly care for now, but it's good to be aware of
the implication.


This patch (of 9):

Let's add three unmerge tests (MADV_UNMERGEABLE unmerging all pages in the
range).

test_unmerge(): basic unmerge tests
test_unmerge_discarded(): have some pte_none() entries in the range
test_unmerge_uffd_wp(): protect the merged pages using uffd-wp

ksm_tests.c currently contains a mixture of benchmarks and tests, whereby
each test is carried out by executing the ksm_tests binary with specific
parameters.  Let's add new ksm_functional_tests.c that performs multiple,
smaller functional tests all at once.

Link: https://lkml.kernel.org/r/20221021101141.84170-1-david@redhat.com
Link: https://lkml.kernel.org/r/20221021101141.84170-5-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/tools/testing/selftests/vm/vm_util.c b/tools/testing/selftests/vm/vm_util.c
index 5bbf7641a0f0..710571902743 100644
--- a/tools/testing/selftests/vm/vm_util.c
+++ b/tools/testing/selftests/vm/vm_util.c
@@ -43,6 +43,16 @@ bool pagemap_is_populated(int fd, char *start)
 	return entry & 0xc000000000000000ull;
 }
 
+unsigned long pagemap_get_pfn(int fd, char *start)
+{
+	uint64_t entry = pagemap_get_entry(fd, start);
+
+	/* If present (63th bit), PFN is at bit 0 -- 54. */
+	if (entry & 0x8000000000000000ull)
+		return entry & 0x007fffffffffffffull;
+	return -1ull;
+}
+
 void clear_softdirty(void)
 {
 	int ret;