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 --- mm/khugepaged.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 5c6015ac7b5e..6df2857d94c6 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -68,7 +68,10 @@ 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; @@ -1267,7 +1270,7 @@ static enum scan_result hpage_collapse_scan_pmd(struct mm_struct *mm, result = find_pmd_or_thp_or_none(mm, start_addr, &pmd); if (result != SCAN_SUCCEED) { if (cur_progress) - *cur_progress = HPAGE_PMD_NR; + *cur_progress = 1; goto out; } @@ -1276,7 +1279,7 @@ static enum scan_result hpage_collapse_scan_pmd(struct mm_struct *mm, pte = pte_offset_map_lock(mm, pmd, start_addr, &ptl); if (!pte) { if (cur_progress) - *cur_progress = HPAGE_PMD_NR; + *cur_progress = 1; result = SCAN_NO_PTE_TABLE; goto out; } @@ -2347,9 +2350,6 @@ static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, unsigned continue; } - if (cur_progress) - *cur_progress += folio_nr_pages(folio); - if (folio_order(folio) == HPAGE_PMD_ORDER && folio->index == start) { /* Maybe PMD-mapped */ @@ -2361,9 +2361,14 @@ static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, unsigned * returning. */ folio_put(folio); + if (cur_progress) + *cur_progress += 1; break; } + if (cur_progress) + *cur_progress += folio_nr_pages(folio); + node = folio_nid(folio); if (hpage_collapse_scan_abort(node, cc)) { result = SCAN_SCAN_ABORT; -- 2.51.0