From: "Kiryl Shutsemau (Meta)" <[email protected]>
collapse_swapin_single_pte() and collapse_max_ptes_swap() swap a range out
and then require smaps to report exactly the count they asked for. Two
things keep that count from arriving.
MADV_PAGEOUT is best effort, so the count often turns up a moment late.
And wait_for_scan() leaves the range eligible for collapsing, so
khugepaged is still working on it. Collapsing reads the swapped-out pages
back in, so the daemon empties the swap as fast as the case fills it. On
arm64 with 64K pages max_ptes_swap is 1024 pages, which is 64M a step, and
the case loses the race:
# Swapout 1024 of 8192 pages... Fail
not ok 10 collapse_max_ptes_swap
Retry for up to two seconds, holding the range out of khugepaged's reach
meanwhile. The collapse each case runs next restores MADV_HUGEPAGE, so
only the setup is affected.
If the pages still won't swap out, skip: no swap, swap too small or full,
a memcg cap or busy writeback. None of that is a kernel bug.
Assisted-by: LLM
Reviewed-by: Muhammad Usama Anjum <[email protected]>
Tested-by: Muhammad Usama Anjum <[email protected]>
Signed-off-by: Kiryl Shutsemau (Meta) <[email protected]>
---
tools/testing/selftests/mm/khugepaged.c | 41 +++++++++++++++++--------
1 file changed, 29 insertions(+), 12 deletions(-)
diff --git a/tools/testing/selftests/mm/khugepaged.c
b/tools/testing/selftests/mm/khugepaged.c
index 73bf07c39145..398430c33872 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -220,6 +220,29 @@ static bool check_swap(void *addr, unsigned long size)
return swap;
}
+static bool swapout_range(void *p, unsigned long size)
+{
+ int i;
+
+ /* keep khugepaged from collapsing the range and swapping it back in */
+ if (madvise(p, size, MADV_NOHUGEPAGE))
+ ksft_exit_fail_perror("madvise(MADV_NOHUGEPAGE)");
+
+ /*
+ * Retry several times because MADV_PAGEOUT is best effort. Sleep
+ * between the retries to give outstanding writeback a chance to
+ * finish.
+ */
+ for (i = 0; i < 40; i++) {
+ if (madvise(p, size, MADV_PAGEOUT))
+ ksft_exit_fail_perror("madvise(MADV_PAGEOUT)");
+ if (check_swap(p, size))
+ return true;
+ usleep(50 * 1000);
+ }
+ return false;
+}
+
static void *alloc_mapping(int nr)
{
void *p;
@@ -823,12 +846,10 @@ static void collapse_swapin_single_pte(struct
collapse_context *c, struct mem_op
ops->fault(p, 0, hpage_pmd_size);
ksft_print_msg("Swapout one page...");
- if (madvise(p, page_size, MADV_PAGEOUT))
- ksft_exit_fail_perror("madvise(MADV_PAGEOUT)");
- if (check_swap(p, page_size)) {
+ if (swapout_range(p, page_size)) {
success("OK");
} else {
- fail("Fail");
+ skip("Could not swap out");
goto out;
}
@@ -849,12 +870,10 @@ static void collapse_max_ptes_swap(struct
collapse_context *c, struct mem_ops *o
ops->fault(p, 0, hpage_pmd_size);
ksft_print_msg("Swapout %d of %d pages...", max_ptes_swap + 1,
hpage_pmd_nr);
- if (madvise(p, (max_ptes_swap + 1) * page_size, MADV_PAGEOUT))
- ksft_exit_fail_perror("madvise(MADV_PAGEOUT)");
- if (check_swap(p, (max_ptes_swap + 1) * page_size)) {
+ if (swapout_range(p, (max_ptes_swap + 1) * page_size)) {
success("OK");
} else {
- fail("Fail");
+ skip("Could not swap out");
goto out;
}
@@ -866,12 +885,10 @@ static void collapse_max_ptes_swap(struct
collapse_context *c, struct mem_ops *o
ops->fault(p, 0, hpage_pmd_size);
ksft_print_msg("Swapout %d of %d pages...", max_ptes_swap,
hpage_pmd_nr);
- if (madvise(p, max_ptes_swap * page_size, MADV_PAGEOUT))
- ksft_exit_fail_perror("madvise(MADV_PAGEOUT)");
- if (check_swap(p, max_ptes_swap * page_size)) {
+ if (swapout_range(p, max_ptes_swap * page_size)) {
success("OK");
} else {
- fail("Fail");
+ skip("Could not swap out");
goto out;
}
--
2.54.0
