mm: numa: Add pte updates, hinting and migration stats
It is tricky to quantify the basic cost of automatic NUMA placement in a
meaningful manner. This patch adds some vmstats that can be used as part
of a basic costing model.
u = basic unit = sizeof(void *)
Ca = cost of struct page access = sizeof(struct page) / u
Cpte = Cost PTE access = Ca
Cupdate = Cost PTE update = (2 * Cpte) + (2 * Wlock)
where Cpte is incurred twice for a read and a write and Wlock
is a constant representing the cost of taking or releasing a
lock
Cnumahint = Cost of a minor page fault = some high constant e.g. 1000
Cpagerw = Cost to read or write a full page = Ca + PAGE_SIZE/u
Ci = Cost of page isolation = Ca + Wi
where Wi is a constant that should reflect the approximate cost
of the locking operation
Cpagecopy = Cpagerw + (Cpagerw * Wnuma) + Ci + (Ci * Wnuma)
where Wnuma is the approximate NUMA factor. 1 is local. 1.2
would imply that remote accesses are 20% more expensive
Balancing cost = Cpte * numa_pte_updates +
Cnumahint * numa_hint_faults +
Ci * numa_pages_migrated +
Cpagecopy * numa_pages_migrated
Note that numa_pages_migrated is used as a measure of how many pages
were isolated even though it would miss pages that failed to migrate. A
vmstat counter could have been added for it but the isolation cost is
pretty marginal in comparison to the overall cost so it seemed overkill.
The ideal way to measure automatic placement benefit would be to count
the number of remote accesses versus local accesses and do something like
benefit = (remote_accesses_before - remove_access_after) * Wnuma
but the information is not readily available. As a workload converges, the
expection would be that the number of remote numa hints would reduce to 0.
convergence = numa_hint_faults_local / numa_hint_faults
where this is measured for the last N number of
numa hints recorded. When the workload is fully
converged the value is 1.
This can measure if the placement policy is converging and how fast it is
doing it.
Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Rik van Riel <riel@redhat.com>
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index ee81337..f3a477f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1026,6 +1026,7 @@
struct page *page = NULL;
unsigned long haddr = addr & HPAGE_PMD_MASK;
int target_nid;
+ int current_nid = -1;
spin_lock(&mm->page_table_lock);
if (unlikely(!pmd_same(pmd, *pmdp)))
@@ -1034,6 +1035,10 @@
page = pmd_page(pmd);
get_page(page);
spin_unlock(&mm->page_table_lock);
+ current_nid = page_to_nid(page);
+ count_vm_numa_event(NUMA_HINT_FAULTS);
+ if (current_nid == numa_node_id())
+ count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
target_nid = mpol_misplaced(page, vma, haddr);
if (target_nid == -1)
diff --git a/mm/memory.c b/mm/memory.c
index 8012c19..8a7b4cc 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3477,6 +3477,7 @@
set_pte_at(mm, addr, ptep, pte);
update_mmu_cache(vma, addr, ptep);
+ count_vm_numa_event(NUMA_HINT_FAULTS);
page = vm_normal_page(vma, addr, pte);
if (!page) {
pte_unmap_unlock(ptep, ptl);
@@ -3485,6 +3486,8 @@
get_page(page);
current_nid = page_to_nid(page);
+ if (current_nid == numa_node_id())
+ count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
target_nid = mpol_misplaced(page, vma, addr);
pte_unmap_unlock(ptep, ptl);
if (target_nid == -1) {
@@ -3517,6 +3520,9 @@
unsigned long offset;
spinlock_t *ptl;
bool numa = false;
+ int local_nid = numa_node_id();
+ unsigned long nr_faults = 0;
+ unsigned long nr_faults_local = 0;
spin_lock(&mm->page_table_lock);
pmd = *pmdp;
@@ -3565,10 +3571,16 @@
curr_nid = page_to_nid(page);
task_numa_fault(curr_nid, 1);
+ nr_faults++;
+ if (curr_nid == local_nid)
+ nr_faults_local++;
+
pte = pte_offset_map_lock(mm, pmdp, addr, &ptl);
}
pte_unmap_unlock(orig_pte, ptl);
+ count_vm_numa_events(NUMA_HINT_FAULTS, nr_faults);
+ count_vm_numa_events(NUMA_HINT_FAULTS_LOCAL, nr_faults_local);
return 0;
}
#else
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index a7a62fe..516491f 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -583,6 +583,8 @@
BUILD_BUG_ON(_PAGE_NUMA != _PAGE_PROTNONE);
nr_updated = change_protection(vma, addr, end, vma->vm_page_prot, 0, 1);
+ if (nr_updated)
+ count_vm_numa_events(NUMA_PTE_UPDATES, nr_updated);
return nr_updated;
}
diff --git a/mm/migrate.c b/mm/migrate.c
index c7d5500..23bba5d 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1514,7 +1514,8 @@
if (nr_remaining) {
putback_lru_pages(&migratepages);
isolated = 0;
- }
+ } else
+ count_vm_numa_event(NUMA_PAGE_MIGRATE);
}
BUG_ON(!list_empty(&migratepages));
out:
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 3a067fa..c0f1f6d 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -774,6 +774,12 @@
"pgrotated",
+#ifdef CONFIG_NUMA_BALANCING
+ "numa_pte_updates",
+ "numa_hint_faults",
+ "numa_hint_faults_local",
+ "numa_pages_migrated",
+#endif
#ifdef CONFIG_MIGRATION
"pgmigrate_success",
"pgmigrate_fail",