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Subject[PATCH 48/52] sched: Refine the 'shared tasks' memory interleaving logic
Date
Change the adaptive memory policy code to take a majority of buddies
on a node into account. Previously, since this commit:

"sched: Track shared task's node groups and interleave their memory allocations"

We'd include any node that has run a buddy in the past, which was too
aggressive and spread the allocations of 'mostly converged' workloads
too much, and prevented their further convergence.

Add a few other variants for testing:

NUMA_POLICY_ADAPTIVE: use memory on every node that runs a buddy of this task

NUMA_POLICY_SYSWIDE: use a simple, static, system-wide mask

NUMA_POLICY_MAXNODE: use memory on this task's 'maximum node'

NUMA_POLICY_MAXBUDDIES: use memory on the node with the most buddies

NUMA_POLICY_MANYBUDDIES: this is the default, a quorum of buddies
determines the allocation mask

The 'many buddies' quorum logic appears to work best in practice,
but the 'maxnode' and 'syswide' ones are good, robust policies too.

[ Also extend the sched_feat() code from 32 to 64 features because
we are hitting that limit on 32-bit CPUs, and address a warning
on !CONFIG_BUG kernels. ]

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/core.c | 6 ++++--
kernel/sched/fair.c | 45 ++++++++++++++++++++++++++++++++++++++-------
kernel/sched/features.h | 6 ++++++
kernel/sched/sched.h | 4 ++--
4 files changed, 50 insertions(+), 11 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 26a2ede..85fd67c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -132,9 +132,9 @@ void update_rq_clock(struct rq *rq)
*/

#define SCHED_FEAT(name, enabled) \
- (1UL << __SCHED_FEAT_##name) * enabled |
+ (1ULL << __SCHED_FEAT_##name) * enabled |

-const_debug unsigned int sysctl_sched_features =
+const_debug u64 sysctl_sched_features =
#include "features.h"
0;

@@ -2833,6 +2833,8 @@ pick_next_task(struct rq *rq)
}

BUG(); /* the idle class will always have a runnable task */
+
+ return NULL; /* if BUG() is a NOP then return NULL to crash the scheduler */
}

/*
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9262692..eaff006 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1611,6 +1611,9 @@ static int sched_update_ideal_cpu_shared(struct task_struct *p, int *flip_tasks)
min_node_load = LONG_MAX;
min_node = -1;

+ if (sched_feat(NUMA_POLICY_MANYBUDDIES))
+ nodes_clear(p->numa_policy.v.nodes);
+
/*
* Map out our maximum buddies layout:
*/
@@ -1677,16 +1680,28 @@ static int sched_update_ideal_cpu_shared(struct task_struct *p, int *flip_tasks)
min_node = node;
}

- if (buddies)
- node_set(node, p->numa_policy.v.nodes);
- else
- node_clear(node, p->numa_policy.v.nodes);
+ if (sched_feat(NUMA_POLICY_ADAPTIVE)) {
+ if (buddies)
+ node_set(node, p->numa_policy.v.nodes);
+ else
+ node_clear(node, p->numa_policy.v.nodes);
+ }
+
+ if (!buddies) {
+ if (sched_feat(NUMA_POLICY_MANYBUDDIES))
+ node_clear(node, p->numa_policy.v.nodes);
+ continue;
+ }
+
+ /* A majority of buddies attracts memory: */
+ if (sched_feat(NUMA_POLICY_MANYBUDDIES)) {
+ if (buddies >= 3)
+ node_set(node, p->numa_policy.v.nodes);
+ }

/* Don't go to a node that is near its capacity limit: */
if (node_load + SCHED_LOAD_SCALE > node_capacity)
continue;
- if (!buddies)
- continue;

if (buddies > max_buddies && target_cpu != -1) {
max_buddies = buddies;
@@ -1696,6 +1711,13 @@ static int sched_update_ideal_cpu_shared(struct task_struct *p, int *flip_tasks)
}
}

+ /* Cluster memory around the buddies maximum: */
+ if (sched_feat(NUMA_POLICY_MAXBUDDIES)) {
+ if (ideal_node != -1) {
+ nodes_clear(p->numa_policy.v.nodes);
+ node_set(ideal_node, p->numa_policy.v.nodes);
+ }
+ }
if (WARN_ON_ONCE(ideal_node == -1 && ideal_cpu != -1))
return this_cpu;
if (WARN_ON_ONCE(ideal_node != -1 && ideal_cpu == -1))
@@ -2079,6 +2101,15 @@ static void task_numa_placement_tick(struct task_struct *p)
p->numa_faults[idx_oldnode] = 0;
}
sched_setnuma(p, ideal_node, shared);
+
+ /* Allocate only the maximum node: */
+ if (sched_feat(NUMA_POLICY_MAXNODE)) {
+ nodes_clear(p->numa_policy.v.nodes);
+ node_set(ideal_node, p->numa_policy.v.nodes);
+ }
+ /* Allocate system-wide: */
+ if (sched_feat(NUMA_POLICY_SYSWIDE))
+ p->numa_policy.v.nodes = node_online_map;
/*
* We changed a node, start scanning more frequently again
* to map out the working set:
@@ -2322,7 +2353,7 @@ void task_numa_scan_work(struct callback_head *work)
}

/* Skip small VMAs. They are not likely to be of relevance */
- if (((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) < HPAGE_PMD_NR) {
+ if (vma->vm_end - vma->vm_start < HPAGE_SIZE) {
end = vma->vm_end;
continue;
}
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index 9075faf..1775b80 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -81,5 +81,11 @@ SCHED_FEAT(NUMA_LB, false)
SCHED_FEAT(NUMA_GROUP_LB_COMPRESS, true)
SCHED_FEAT(NUMA_GROUP_LB_SPREAD, true)
SCHED_FEAT(MIGRATE_FAULT_STATS, false)
+SCHED_FEAT(NUMA_POLICY_ADAPTIVE, false)
+SCHED_FEAT(NUMA_POLICY_SYSWIDE, false)
+SCHED_FEAT(NUMA_POLICY_MAXNODE, false)
+SCHED_FEAT(NUMA_POLICY_MAXBUDDIES, false)
+SCHED_FEAT(NUMA_POLICY_MANYBUDDIES, true)
+
SCHED_FEAT(NUMA_CONVERGE_MIGRATIONS, true)
#endif
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 733f646..0fdd304 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -648,7 +648,7 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu)
# define const_debug const
#endif

-extern const_debug unsigned int sysctl_sched_features;
+extern const_debug u64 sysctl_sched_features;

#define SCHED_FEAT(name, enabled) \
__SCHED_FEAT_##name ,
@@ -684,7 +684,7 @@ static __always_inline bool static_branch_##name(struct static_key *key) \
extern struct static_key sched_feat_keys[__SCHED_FEAT_NR];
#define sched_feat(x) (static_branch_##x(&sched_feat_keys[__SCHED_FEAT_##x]))
#else /* !(SCHED_DEBUG && HAVE_JUMP_LABEL) */
-#define sched_feat(x) (sysctl_sched_features & (1UL << __SCHED_FEAT_##x))
+#define sched_feat(x) (sysctl_sched_features & (1ULL << __SCHED_FEAT_##x))
#endif /* SCHED_DEBUG && HAVE_JUMP_LABEL */

#ifdef CONFIG_NUMA_BALANCING
--
1.7.11.7


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