From: Yang Yang Subject: mm/vmstat: add events for ksm cow Users may use ksm by calling madvise(, , MADV_MERGEABLE) when they want to save memory, it's a tradeoff by suffering delay on ksm cow. Users can get to know how much memory ksm saved by reading /sys/kernel/mm/ksm/pages_sharing, but they don't know what's the costs of ksm cow, and this is important of some delay sensitive tasks. So add ksm cow events to help users evaluate whether or how to use ksm. Also update Documentation/admin-guide/mm/ksm.rst with new added events. Link: https://lkml.kernel.org/r/20220331035616.2390805-1-yang.yang29@zte.com.cn Signed-off-by: Yang Yang Reviewed-by: David Hildenbrand Reviewed-by: xu xin Reviewed-by: Ran Xiaokai Cc: Matthew Wilcox (Oracle) Cc: Jonathan Corbet Cc: Dave Hansen Cc: Saravanan D Cc: Minchan Kim Cc: John Hubbard Signed-off-by: Andrew Morton --- Documentation/admin-guide/mm/ksm.rst | 18 ++++++++++++++++++ include/linux/vm_event_item.h | 3 +++ mm/memory.c | 4 ++++ mm/vmstat.c | 3 +++ 4 files changed, 28 insertions(+) --- a/Documentation/admin-guide/mm/ksm.rst~mm-vmstat-add-events-for-ksm-cow +++ a/Documentation/admin-guide/mm/ksm.rst @@ -184,6 +184,24 @@ The maximum possible ``pages_sharing/pag ``max_page_sharing`` tunable. To increase the ratio ``max_page_sharing`` must be increased accordingly. +Monitoring KSM events +===================== + +There are some counters in /proc/vmstat that may be used to monitor KSM events. +KSM might help save memory, it's a tradeoff by may suffering delay on KSM COW +or on swapping in copy. Those events could help users evaluate whether or how +to use KSM. For example, if cow_ksm increases too fast, user may decrease the +range of madvise(, , MADV_MERGEABLE). + +cow_ksm + is incremented every time a KSM page triggers copy on write (COW) + when users try to write to a KSM page, we have to make a copy. + +ksm_swpin_copy + is incremented every time a KSM page is copied when swapping in + note that KSM page might be copied when swapping in because do_swap_page() + cannot do all the locking needed to reconstitute a cross-anon_vma KSM page. + -- Izik Eidus, Hugh Dickins, 17 Nov 2009 --- a/include/linux/vm_event_item.h~mm-vmstat-add-events-for-ksm-cow +++ a/include/linux/vm_event_item.h @@ -133,6 +133,9 @@ enum vm_event_item { PGPGIN, PGPGOUT, PS KSM_SWPIN_COPY, #endif #endif +#ifdef CONFIG_KSM + COW_KSM, +#endif #ifdef CONFIG_X86 DIRECT_MAP_LEVEL2_SPLIT, DIRECT_MAP_LEVEL3_SPLIT, --- a/mm/memory.c~mm-vmstat-add-events-for-ksm-cow +++ a/mm/memory.c @@ -3456,6 +3456,10 @@ copy: get_page(vmf->page); pte_unmap_unlock(vmf->pte, vmf->ptl); +#ifdef CONFIG_KSM + if (PageKsm(vmf->page)) + count_vm_event(COW_KSM); +#endif return wp_page_copy(vmf); } --- a/mm/vmstat.c~mm-vmstat-add-events-for-ksm-cow +++ a/mm/vmstat.c @@ -1393,6 +1393,9 @@ const char * const vmstat_text[] = { "ksm_swpin_copy", #endif #endif +#ifdef CONFIG_KSM + "cow_ksm", +#endif #ifdef CONFIG_X86 "direct_map_level2_splits", "direct_map_level3_splits", _