selftests/vm: anon_cow: test COW handling of anonymous memory

Patch series "selftests/vm: test COW handling of anonymous memory".

This is my current set of tests for testing COW handling of anonymous
memory, especially when interacting with GUP.  I developed these tests
while working on PageAnonExclusive and managed to clean them up just now.

On current upstream Linux, all tests pass except the hugetlb tests that
rely on vmsplice -- these tests should pass as soon as vmsplice properly
uses FOLL_PIN instead of FOLL_GET.

I'm working on additional tests for COW handling in private mappings,
focusing on long-term R/O pinning e.g., of the shared zeropage, pagecache
pages and KSM pages.  These tests, however, will go into a different file.
So this is everything I have regarding tests for anonymous memory.


This patch (of 7):

Let's start adding tests for our COW handling of anonymous memory.  We'll
focus on basic tests that we can achieve without additional libraries or
gup_test extensions.

We'll add THP and hugetlb tests separately.

[[email protected]: s/size_t/ssize_t/ on `cur', `total', `transferred';]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: David Hildenbrand <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Christoph von Recklinghausen <[email protected]>
Cc: Don Dutile <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Nadav Amit <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

tools/testing/selftests/vm/.gitignore

@@ -1,4 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0-only
+anon_cow
 hugepage-mmap
 hugepage-mremap
 hugepage-shm

tools/testing/selftests/vm/Makefile

@@ -25,7 +25,8 @@ MAKEFLAGS += --no-builtin-rules
 
 CFLAGS = -Wall -I $(top_srcdir) -I $(top_srcdir)/usr/include $(EXTRA_CFLAGS) $(KHDR_INCLUDES)
 LDLIBS = -lrt -lpthread
-TEST_GEN_FILES = compaction_test
+TEST_GEN_FILES = anon_cow
+TEST_GEN_FILES += compaction_test
 TEST_GEN_FILES += gup_test
 TEST_GEN_FILES += hmm-tests
 TEST_GEN_FILES += hugetlb-madvise
@@ -95,6 +96,7 @@ TEST_FILES += va_128TBswitch.sh
 
 include ../lib.mk
 
+$(OUTPUT)/anon_cow: vm_util.c
 $(OUTPUT)/khugepaged: vm_util.c
 $(OUTPUT)/madv_populate: vm_util.c
 $(OUTPUT)/soft-dirty: vm_util.c