From 575299ea18a8c0575d4c2ef6ad3fa4d41d529d1c Mon Sep 17 00:00:00 2001 From: Saravanan D Date: Tue, 4 May 2021 18:38:03 -0700 Subject: x86/mm: track linear mapping split events To help with debugging the sluggishness caused by TLB miss/reload, we introduce monotonic hugepage [direct mapped] split event counts since system state: SYSTEM_RUNNING to be displayed as part of /proc/vmstat in x86 servers The lifetime split event information will be displayed at the bottom of /proc/vmstat .... swap_ra 0 swap_ra_hit 0 direct_map_level2_splits 94 direct_map_level3_splits 4 nr_unstable 0 .... One of the many lasting sources of direct hugepage splits is kernel tracing (kprobes, tracepoints). Note that the kernel's code segment [512 MB] points to the same physical addresses that have been already mapped in the kernel's direct mapping range. Source : Documentation/x86/x86_64/mm.rst When we enable kernel tracing, the kernel has to modify attributes/permissions of the text segment hugepages that are direct mapped causing them to split. Kernel's direct mapped hugepages do not coalesce back after split and remain in place for the remainder of the lifetime. An instance of direct page splits when we turn on dynamic kernel tracing .... cat /proc/vmstat | grep -i direct_map_level direct_map_level2_splits 784 direct_map_level3_splits 12 bpftrace -e 'tracepoint:raw_syscalls:sys_enter { @ [pid, comm] = count(); }' cat /proc/vmstat | grep -i direct_map_level direct_map_level2_splits 789 direct_map_level3_splits 12 .... Link: https://lkml.kernel.org/r/20210218235744.1040634-1-saravanand@fb.com Signed-off-by: Saravanan D Acked-by: Tejun Heo Acked-by: Johannes Weiner Acked-by: Dave Hansen Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/x86/mm/pat/set_memory.c | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'arch') diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c index 427980617557..156cd235659f 100644 --- a/arch/x86/mm/pat/set_memory.c +++ b/arch/x86/mm/pat/set_memory.c @@ -16,6 +16,8 @@ #include #include #include +#include +#include #include #include @@ -91,6 +93,12 @@ static void split_page_count(int level) return; direct_pages_count[level]--; + if (system_state == SYSTEM_RUNNING) { + if (level == PG_LEVEL_2M) + count_vm_event(DIRECT_MAP_LEVEL2_SPLIT); + else if (level == PG_LEVEL_1G) + count_vm_event(DIRECT_MAP_LEVEL3_SPLIT); + } direct_pages_count[level - 1] += PTRS_PER_PTE; } -- cgit v1.2.3