To help with debugging the sluggishness caused by TLB miss/reload, we introduce monotonic lifetime hugepage 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_2M_splits 167 direct_map_1G_splits 6 nr_unstable 0 .... One of the many lasting (as we don't coalesce back) sources for huge page splits is tracing as the granular page attribute/permission changes would force the kernel to split code segments mapped to huge pages to smaller ones thereby increasing the probability of TLB miss/reload even after tracing has been stopped. Signed-off-by: Saravanan D <saravan...@fb.com> --- arch/x86/mm/pat/set_memory.c | 18 ++++++++++++++++++ include/linux/vm_event_item.h | 8 ++++++++ mm/vmstat.c | 8 ++++++++ 3 files changed, 34 insertions(+) diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c index 16f878c26667..3ea6316df089 100644 --- a/arch/x86/mm/pat/set_memory.c +++ b/arch/x86/mm/pat/set_memory.c @@ -16,6 +16,8 @@ #include <linux/pci.h> #include <linux/vmalloc.h> #include <linux/libnvdimm.h> +#include <linux/vmstat.h> +#include <linux/kernel.h> #include <asm/e820/api.h> #include <asm/processor.h> @@ -85,12 +87,28 @@ void update_page_count(int level, unsigned long pages) spin_unlock(&pgd_lock); } +void update_split_page_event_count(int level) +{ + if (system_state == SYSTEM_RUNNING) { + if (level == PG_LEVEL_2M) { +#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE) + count_vm_event(DIRECT_MAP_2M_SPLIT); +#else + count_vm_event(DIRECT_MAP_4M_SPLIT); +#endif + } else if (level == PG_LEVEL_1G) { + count_vm_event(DIRECT_MAP_1G_SPLIT); + } + } +} + static void split_page_count(int level) { if (direct_pages_count[level] == 0) return; direct_pages_count[level]--; + update_split_page_event_count(level); direct_pages_count[level - 1] += PTRS_PER_PTE; } diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h index 18e75974d4e3..439742d2435e 100644 --- a/include/linux/vm_event_item.h +++ b/include/linux/vm_event_item.h @@ -120,6 +120,14 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT, #ifdef CONFIG_SWAP SWAP_RA, SWAP_RA_HIT, +#endif +#if defined(__x86_64__) +#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE) + DIRECT_MAP_2M_SPLIT, +#else + DIRECT_MAP_4M_SPLIT, +#endif + DIRECT_MAP_1G_SPLIT, #endif NR_VM_EVENT_ITEMS }; diff --git a/mm/vmstat.c b/mm/vmstat.c index f8942160fc95..beaa2bb4f9dc 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1350,6 +1350,14 @@ const char * const vmstat_text[] = { "swap_ra", "swap_ra_hit", #endif +#if defined(__x86_64__) +#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE) + "direct_map_2M_splits", +#else + "direct_map_4M_splits", +#endif + "direct_map_1G_splits", +#endif #endif /* CONFIG_VM_EVENT_COUNTERS || CONFIG_MEMCG */ }; #endif /* CONFIG_PROC_FS || CONFIG_SYSFS || CONFIG_NUMA || CONFIG_MEMCG */ -- 2.24.1