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 | 23 ++++++++++++++++++----- 1 file changed, 18 insertions(+), 5 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 9f99f61689f8..2b3685b195f5 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; @@ -2487,12 +2490,22 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result, khugepaged_scan.address, &mmap_locked, cc); } - if (*result == SCAN_SUCCEED) - ++khugepaged_pages_collapsed; - /* move to next address */ khugepaged_scan.address += HPAGE_PMD_SIZE; - progress += HPAGE_PMD_NR; + + switch (*result) { + case SCAN_NO_PTE_TABLE: + case SCAN_PMD_MAPPED: + case SCAN_PTE_MAPPED_HUGEPAGE: + progress++; + break; + case SCAN_SUCCEED: + ++khugepaged_pages_collapsed; + fallthrough; + default: + progress += HPAGE_PMD_NR; + } + if (!mmap_locked) /* * We released mmap_lock so break loop. Note -- 2.51.0