From: Vernon Yang Date: Sat, 21 Feb 2026 09:39:15 +0000 (+0800) Subject: mm: khugepaged: add trace_mm_khugepaged_scan event X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=36cec70e4acbae21e39527c1d41083bca148c7c8;p=thirdparty%2Flinux.git mm: khugepaged: add trace_mm_khugepaged_scan event Patch series "Improve khugepaged scan logic", v8. This series improves the khugepaged scan logic and reduces CPU consumption by prioritizing scanning tasks that access memory frequently. The following data is traced by bpftrace[1] 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 has below phenomenon: the khugepaged list is scanned in a FIFO manner, as long as the task is not destroyed, 1. the task no longer has memory that can be collapsed into hugepage, continues scan it always. 2. the task at the front of the khugepaged scan list is cold, they are still scanned first. 3. everyone scan at intervals of khugepaged_scan_sleep_millisecs (default 10s). If we always scan the above two cases first, the valid scan will have to wait for a long time. For the first case, when the memory is either SCAN_PMD_MAPPED or SCAN_NO_PTE_TABLE or SCAN_PTE_MAPPED_HUGEPAGE [5], just skip it. For the second case, if the user has explicitly informed us via MADV_FREE that these folios will be freed, just skip it only. The below is some performance test results. kernbench results (testing on x86_64 machine): baseline w/o patches test w/ patches Amean user-32 18522.51 ( 0.00%) 18333.64 * 1.02%* Amean syst-32 1137.96 ( 0.00%) 1113.79 * 2.12%* Amean elsp-32 666.04 ( 0.00%) 659.44 * 0.99%* BAmean-95 user-32 18520.01 ( 0.00%) 18323.57 ( 1.06%) BAmean-95 syst-32 1137.68 ( 0.00%) 1110.50 ( 2.39%) BAmean-95 elsp-32 665.92 ( 0.00%) 659.06 ( 1.03%) BAmean-99 user-32 18520.01 ( 0.00%) 18323.57 ( 1.06%) BAmean-99 syst-32 1137.68 ( 0.00%) 1110.50 ( 2.39%) BAmean-99 elsp-32 665.92 ( 0.00%) 659.06 ( 1.03%) Create three task[2]: hot1 -> cold -> hot2. After all three task are created, each allocate memory 128MB. the hot1/hot2 task continuously access 128 MB memory, while the cold task only accesses its memory briefly andthen call madvise(MADV_FREE). Here are the performance test results: (Throughput bigger is better, other smaller is better) Testing on x86_64 machine: | task hot2 | without patch | with patch | delta | |---------------------|---------------|---------------|---------| | total accesses time | 3.14 sec | 2.93 sec | -6.69% | | cycles per access | 4.96 | 2.21 | -55.44% | | Throughput | 104.38 M/sec | 111.89 M/sec | +7.19% | | dTLB-load-misses | 284814532 | 69597236 | -75.56% | Testing on qemu-system-x86_64 -enable-kvm: | task hot2 | without patch | with patch | delta | |---------------------|---------------|---------------|---------| | total accesses time | 3.35 sec | 2.96 sec | -11.64% | | cycles per access | 7.29 | 2.07 | -71.60% | | Throughput | 97.67 M/sec | 110.77 M/sec | +13.41% | | dTLB-load-misses | 241600871 | 3216108 | -98.67% | This patch (of 4): Add mm_khugepaged_scan event to track the total time for full scan and the total number of pages scanned of khugepaged. Link: https://lkml.kernel.org/r/20260221093918.1456187-2-vernon2gm@gmail.com Signed-off-by: Vernon Yang Acked-by: David Hildenbrand (Red Hat) Reviewed-by: Barry Song Reviewed-by: Lance Yang Reviewed-by: Dev Jain Cc: Baolin Wang Cc: Dev Jain Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Cc: Nico Pache Cc: Ryan Roberts Cc: Steven Rostedt Cc: Zi Yan Signed-off-by: Andrew Morton --- diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h index 4e41bff318888..384e29f6bef0f 100644 --- a/include/trace/events/huge_memory.h +++ b/include/trace/events/huge_memory.h @@ -237,5 +237,30 @@ TRACE_EVENT(mm_khugepaged_collapse_file, __print_symbolic(__entry->result, SCAN_STATUS)) ); +TRACE_EVENT(mm_khugepaged_scan, + + TP_PROTO(struct mm_struct *mm, unsigned int progress, + bool full_scan_finished), + + TP_ARGS(mm, progress, full_scan_finished), + + TP_STRUCT__entry( + __field(struct mm_struct *, mm) + __field(unsigned int, progress) + __field(bool, full_scan_finished) + ), + + TP_fast_assign( + __entry->mm = mm; + __entry->progress = progress; + __entry->full_scan_finished = full_scan_finished; + ), + + TP_printk("mm=%p, progress=%u, full_scan_finished=%d", + __entry->mm, + __entry->progress, + __entry->full_scan_finished) +); + #endif /* __HUGE_MEMORY_H */ #include diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 17ab58681032b..4d7baf220ad9d 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2527,6 +2527,8 @@ breakouterloop_mmap_lock: collect_mm_slot(slot); } + trace_mm_khugepaged_scan(mm, progress, khugepaged_scan.mm_slot == NULL); + return progress; }