| Message ID | 20210128233430.1460964-1-saravanand@fb.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [V6] x86/mm: Tracking linear mapping split events | expand |
On Thu, Jan 28, 2021 at 03:34:30PM -0800, Saravanan D wrote: > 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 ... > Signed-off-by: Saravanan D <saravanand@fb.com> Acked-by: Tejun Heo <tj@kernel.org> Thanks.
On Thu, Jan 28, 2021 at 03:34:30PM -0800, Saravanan D wrote: > 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 > .... > > Signed-off-by: Saravanan D <saravanand@fb.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Hi all, So far I have received two acks for V6 version of my patch > Acked-by: Tejun Heo <tj@kernel.org> > Acked-by: Johannes Weiner <hannes@cmpxchg.org> Are there any more objections ? Thanks, Saravanan D
On 1/28/21 3:34 PM, Saravanan D wrote: > > 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. Looks fine to me: Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c index 16f878c26667..a7b3c5f1d316 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> @@ -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; } diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h index 18e75974d4e3..7c06c2bdc33b 100644 --- a/include/linux/vm_event_item.h +++ b/include/linux/vm_event_item.h @@ -120,6 +120,10 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT, #ifdef CONFIG_SWAP SWAP_RA, SWAP_RA_HIT, +#endif +#ifdef CONFIG_X86 + DIRECT_MAP_LEVEL2_SPLIT, + DIRECT_MAP_LEVEL3_SPLIT, #endif NR_VM_EVENT_ITEMS }; diff --git a/mm/vmstat.c b/mm/vmstat.c index f8942160fc95..a43ac4ac98a2 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1350,6 +1350,10 @@ const char * const vmstat_text[] = { "swap_ra", "swap_ra_hit", #endif +#ifdef CONFIG_X86 + "direct_map_level2_splits", + "direct_map_level3_splits", +#endif #endif /* CONFIG_VM_EVENT_COUNTERS || CONFIG_MEMCG */ }; #endif /* CONFIG_PROC_FS || CONFIG_SYSFS || CONFIG_NUMA || CONFIG_MEMCG */
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 .... Signed-off-by: Saravanan D <saravanand@fb.com> --- arch/x86/mm/pat/set_memory.c | 8 ++++++++ include/linux/vm_event_item.h | 4 ++++ mm/vmstat.c | 4 ++++ 3 files changed, 16 insertions(+)