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authorSaravanan D <saravanand@fb.com>2021-05-05 04:38:03 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2021-05-05 21:27:25 +0300
commit575299ea18a8c0575d4c2ef6ad3fa4d41d529d1c (patch)
tree126118dca3a748070762f9eb8b0ad68e11e7f69b /mm/vmstat.c
parentc675790972916d3722809fcc52c5c4f8421b2e5d (diff)
downloadlinux-575299ea18a8c0575d4c2ef6ad3fa4d41d529d1c.tar.xz
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 <saravanand@fb.com> Acked-by: Tejun Heo <tj@kernel.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Dave Hansen <dave.hansen@linux.intel.com> Cc: Ingo Molnar <mingo@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/vmstat.c')
-rw-r--r--mm/vmstat.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 06cd78dc914d..5ba118521ded 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1369,6 +1369,10 @@ 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 */