The patch titled
Subject: selftests/vm: add test to measure MADV_UNMERGEABLE performance
has been added to the -mm mm-unstable branch. Its filename is
selftests-vm-add-test-to-measure-madv_unmergeable-performance.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-vm-add-test-to-measure-madv_unmergeable-performance.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: selftests/vm: add test to measure MADV_UNMERGEABLE performance
Date: Fri, 30 Sep 2022 16:19:25 +0200
Patch series "mm/ksm: break_ksm() cleanups and fixes".
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.
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 ~8% -- 9% (old: ~5250 MiB/s, new: ~4800 MiB/s). I don't
think we particularly care for now, but it's good to be aware of the
implication.
This patch (of 7):
Let's add a test to measure performance of KSM breaking not triggered via
COW, but triggered by disabling KSM on an area filled with KSM pages via
MADV_UNMERGEABLE.
Link: https://lkml.kernel.org/r/20220930141931.174362-1-david@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20220930141931.174362-2-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Peter Xu <peterx@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
tools/testing/selftests/vm/ksm_tests.c | 76 ++++++++++++++++++++++-
1 file changed, 74 insertions(+), 2 deletions(-)
--- a/tools/testing/selftests/vm/ksm_tests.c~selftests-vm-add-test-to-measure-madv_unmergeable-performance
+++ a/tools/testing/selftests/vm/ksm_tests.c
@@ -40,6 +40,7 @@ enum ksm_test_name {
CHECK_KSM_NUMA_MERGE,
KSM_MERGE_TIME,
KSM_MERGE_TIME_HUGE_PAGES,
+ KSM_UNMERGE_TIME,
KSM_COW_TIME
};
@@ -108,7 +109,10 @@ static void print_help(void)
" -P evaluate merging time and speed.\n"
" For this test, the size of duplicated memory area (in MiB)\n"
" must be provided using -s option\n"
- " -H evaluate merging time and speed of area allocated mostly with huge pages\n"
+ " -H evaluate merging time and speed of area allocated mostly with huge pages\n"
+ " For this test, the size of duplicated memory area (in MiB)\n"
+ " must be provided using -s option\n"
+ " -D evaluate unmerging time and speed when disabling KSM.\n"
" For this test, the size of duplicated memory area (in MiB)\n"
" must be provided using -s option\n"
" -C evaluate the time required to break COW of merged pages.\n\n");
@@ -188,6 +192,16 @@ static int ksm_merge_pages(void *addr, s
return 0;
}
+static int ksm_unmerge_pages(void *addr, size_t size,
+ struct timespec start_time, int timeout)
+{
+ if (madvise(addr, size, MADV_UNMERGEABLE)) {
+ perror("madvise");
+ return 1;
+ }
+ return 0;
+}
+
static bool assert_ksm_pages_count(long dupl_page_count)
{
unsigned long max_page_sharing, pages_sharing, pages_shared;
@@ -560,6 +574,53 @@ err_out:
return KSFT_FAIL;
}
+static int ksm_unmerge_time(int mapping, int prot, int timeout, size_t map_size)
+{
+ void *map_ptr;
+ struct timespec start_time, end_time;
+ unsigned long scan_time_ns;
+
+ map_size *= MB;
+
+ map_ptr = allocate_memory(NULL, prot, mapping, '*', map_size);
+ if (!map_ptr)
+ return KSFT_FAIL;
+ if (clock_gettime(CLOCK_MONOTONIC_RAW, &start_time)) {
+ perror("clock_gettime");
+ goto err_out;
+ }
+ if (ksm_merge_pages(map_ptr, map_size, start_time, timeout))
+ goto err_out;
+
+ if (clock_gettime(CLOCK_MONOTONIC_RAW, &start_time)) {
+ perror("clock_gettime");
+ goto err_out;
+ }
+ if (ksm_unmerge_pages(map_ptr, map_size, start_time, timeout))
+ goto err_out;
+ if (clock_gettime(CLOCK_MONOTONIC_RAW, &end_time)) {
+ perror("clock_gettime");
+ goto err_out;
+ }
+
+ scan_time_ns = (end_time.tv_sec - start_time.tv_sec) * NSEC_PER_SEC +
+ (end_time.tv_nsec - start_time.tv_nsec);
+
+ printf("Total size: %lu MiB\n", map_size / MB);
+ printf("Total time: %ld.%09ld s\n", scan_time_ns / NSEC_PER_SEC,
+ scan_time_ns % NSEC_PER_SEC);
+ printf("Average speed: %.3f MiB/s\n", (map_size / MB) /
+ ((double)scan_time_ns / NSEC_PER_SEC));
+
+ munmap(map_ptr, map_size);
+ return KSFT_PASS;
+
+err_out:
+ printf("Not OK\n");
+ munmap(map_ptr, map_size);
+ return KSFT_FAIL;
+}
+
static int ksm_cow_time(int mapping, int prot, int timeout, size_t page_size)
{
void *map_ptr;
@@ -644,7 +705,7 @@ int main(int argc, char *argv[])
bool merge_across_nodes = KSM_MERGE_ACROSS_NODES_DEFAULT;
long size_MB = 0;
- while ((opt = getopt(argc, argv, "ha:p:l:z:m:s:MUZNPCH")) != -1) {
+ while ((opt = getopt(argc, argv, "ha:p:l:z:m:s:MUZNPCHD")) != -1) {
switch (opt) {
case 'a':
prot = str_to_prot(optarg);
@@ -701,6 +762,9 @@ int main(int argc, char *argv[])
case 'H':
test_name = KSM_MERGE_TIME_HUGE_PAGES;
break;
+ case 'D':
+ test_name = KSM_UNMERGE_TIME;
+ break;
case 'C':
test_name = KSM_COW_TIME;
break;
@@ -762,6 +826,14 @@ int main(int argc, char *argv[])
ret = ksm_merge_hugepages_time(MAP_PRIVATE | MAP_ANONYMOUS, prot,
ksm_scan_limit_sec, size_MB);
break;
+ case KSM_UNMERGE_TIME:
+ if (size_MB == 0) {
+ printf("Option '-s' is required.\n");
+ return KSFT_FAIL;
+ }
+ ret = ksm_unmerge_time(MAP_PRIVATE | MAP_ANONYMOUS, prot,
+ ksm_scan_limit_sec, size_MB);
+ break;
case KSM_COW_TIME:
ret = ksm_cow_time(MAP_PRIVATE | MAP_ANONYMOUS, prot, ksm_scan_limit_sec,
page_size);
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
selftests-vm-add-test-to-measure-madv_unmergeable-performance.patch
mm-ksm-simplify-break_ksm-to-not-rely-on-vm_fault_write.patch
mm-remove-vm_fault_write.patch
mm-ksm-fix-ksm-cow-breaking-with-userfaultfd-wp-via-fault_flag_unshare.patch
mm-pagewalk-add-walk_page_range_vma.patch
mm-ksm-convert-break_ksm-to-use-walk_page_range_vma.patch
mm-gup-remove-foll_migration.patch
