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 MADV_HUGEPAGE behind, so khugepaged is still
working on the range. Collapsing a range with up to max_ptes_swap pages
swapped out means reading them 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:
# Swapout 1024 of 8192 pages... Fail
not ok 10 collapse_max_ptes_swap
Ask again for up to two seconds, with the range held out of the daemon's
reach while asking. The collapse each case runs next puts MADV_HUGEPAGE
back, so only the setup is affected.
If the pages still will not go, skip. A machine with no swap, or swap too
small, full, capped by a memcg or busy with writeback, is not the kernel
under test refusing. An error from madvise() itself still ends the run.
Assisted-by: Claude-Code:claude-opus-5
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 | 53 +++++++++++++++++++------
1 file changed, 41 insertions(+), 12 deletions(-)
diff --git a/tools/testing/selftests/mm/khugepaged.c
b/tools/testing/selftests/mm/khugepaged.c
index ec5c36a19d92..7eb9db0005a0 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -219,6 +219,41 @@ static bool check_swap(void *addr, unsigned long size)
return swap;
}
+/*
+ * Page the range out and wait for the swap count to say so.
+ *
+ * Two things get in the way. MADV_PAGEOUT is best effort:
+ * shrink_folio_list() leaves a folio alone when it cannot reclaim it right
+ * away, and one still under writeback from an earlier pageout is the common
+ * case, so the count the caller asks for arrives a moment later. And a range
+ * an earlier collapse left MADV_HUGEPAGE is one khugepaged is still working
+ * on: collapsing a range with up to max_ptes_swap pages swapped out means
+ * reading those pages back in, so the daemon undoes the pageout as fast as it
+ * is asked for. Keep the range out of its reach; the collapse the caller runs
+ * next puts MADV_HUGEPAGE back.
+ *
+ * Failing to get the pages out is the machine's answer, not the kernel's --
+ * swap too small, swap full, a memcg cap, a folio still under writeback -- so
+ * callers skip rather than fail. An error from madvise() is different, and
+ * ends the run here.
+ */
+static bool swapout_range(void *p, unsigned long size)
+{
+ int i;
+
+ if (madvise(p, size, MADV_NOHUGEPAGE))
+ ksft_exit_fail_perror("madvise(MADV_NOHUGEPAGE)");
+
+ 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;
@@ -827,12 +862,10 @@ 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;
}
@@ -853,12 +886,10 @@ 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;
}
@@ -870,12 +901,10 @@ 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
