The following data is traced by bpftrace on a desktop system. After
the system has been left idle for 10 minutes upon booting, a lot of
SCAN_PMD_MAPPED or SCAN_NO_PTE_TABLE are observed during a full scan
by khugepaged.
@scan_pmd_status[1]: 1 ## SCAN_SUCCEED
@scan_pmd_status[6]: 2 ## SCAN_EXCEED_SHARED_PTE
@scan_pmd_status[3]: 142 ## SCAN_PMD_MAPPED
@scan_pmd_status[2]: 178 ## SCAN_NO_PTE_TABLE
total progress size: 674 MB
Total time : 419 seconds ## include khugepaged_scan_sleep_millisecs
The khugepaged_scan list save all task that support collapse into hugepage,
as long as the task is not destroyed, khugepaged will not remove it from
the khugepaged_scan list. This exist a phenomenon where task has already
collapsed all memory regions into hugepage, but khugepaged continues to
scan it, which wastes CPU time and invalid, and due to
khugepaged_scan_sleep_millisecs (default 10s) causes a long wait for
scanning a large number of invalid task, so scanning really valid task
is later.
After applying this patch, when the memory is either SCAN_PMD_MAPPED or
SCAN_NO_PTE_TABLE, just skip it, as follow:
@scan_pmd_status[6]: 2
@scan_pmd_status[3]: 147
@scan_pmd_status[2]: 173
total progress size: 45 MB
Total time : 20 seconds
Signed-off-by: Vernon Yang <yanglincheng@kylinos.cn>
---
mm/khugepaged.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 4b124e854e2e..30786c706c4a 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -66,7 +66,10 @@ enum scan_result {
static struct task_struct *khugepaged_thread __read_mostly;
static DEFINE_MUTEX(khugepaged_mutex);
-/* default scan 8*HPAGE_PMD_NR ptes (or vmas) every 10 second */
+/*
+ * default scan 8*HPAGE_PMD_NR ptes, pmd_mapped, no_pte_table or vmas
+ * every 10 second.
+ */
static unsigned int khugepaged_pages_to_scan __read_mostly;
static unsigned int khugepaged_pages_collapsed;
static unsigned int khugepaged_full_scans;
@@ -1264,7 +1267,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
result = find_pmd_or_thp_or_none(mm, start_addr, &pmd);
if (result != SCAN_SUCCEED) {
- _progress = HPAGE_PMD_NR;
+ _progress = 1;
goto out;
}
@@ -1272,7 +1275,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
nodes_clear(cc->alloc_nmask);
pte = pte_offset_map_lock(mm, pmd, start_addr, &ptl);
if (!pte) {
- _progress = HPAGE_PMD_NR;
+ _progress = 1;
result = SCAN_NO_PTE_TABLE;
goto out;
}
@@ -2336,8 +2339,6 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
continue;
}
- _progress += folio_nr_pages(folio);
-
if (folio_order(folio) == HPAGE_PMD_ORDER &&
folio->index == start) {
/* Maybe PMD-mapped */
@@ -2349,9 +2350,12 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
* returning.
*/
folio_put(folio);
+ _progress++;
break;
}
+ _progress += folio_nr_pages(folio);
+
node = folio_nid(folio);
if (hpage_collapse_scan_abort(node, cc)) {
result = SCAN_SCAN_ABORT;
--
2.51.0