* Mel Gorman <mgorman@xxxxxxx> wrote:
> While it is desirable that all threads in a process run on its home
> node, this is not always possible or necessary. There may be more
> threads than exist within the node or the node might over-subscribed
> with unrelated processes.
>
> This can cause a situation whereby a page gets migrated off its home
> node because the threads clearing pte_numa were running off-node. This
> patch uses page->last_nid to build a two-stage filter before pages get
> migrated to avoid problems with short or unlikely task<->node
> relationships.
>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> ---
> mm/mempolicy.c | 30 +++++++++++++++++++++++++++++-
> 1 file changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 4c1c8d8..fd20e28 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -2317,9 +2317,37 @@ int mpol_misplaced(struct page *page, struct vm_area_struct *vma, unsigned long
> }
>
> /* Migrate the page towards the node whose CPU is referencing it */
> - if (pol->flags & MPOL_F_MORON)
> + if (pol->flags & MPOL_F_MORON) {
> + int last_nid;
> +
> polnid = numa_node_id();
>
> + /*
> + * Multi-stage node selection is used in conjunction
> + * with a periodic migration fault to build a temporal
> + * task<->page relation. By using a two-stage filter we
> + * remove short/unlikely relations.
> + *
> + * Using P(p) ~ n_p / n_t as per frequentist
> + * probability, we can equate a task's usage of a
> + * particular page (n_p) per total usage of this
> + * page (n_t) (in a given time-span) to a probability.
> + *
> + * Our periodic faults will sample this probability and
> + * getting the same result twice in a row, given these
> + * samples are fully independent, is then given by
> + * P(n)^2, provided our sample period is sufficiently
> + * short compared to the usage pattern.
> + *
> + * This quadric squishes small probabilities, making
> + * it less likely we act on an unlikely task<->page
> + * relation.
> + */
> + last_nid = page_xchg_last_nid(page, polnid);
> + if (last_nid != polnid)
> + goto out;
> + }
> +
> if (curnid != polnid)
> ret = polnid;
> out:
As mentioned in my other mail, this patch of yours looks very
similar to the numa/core commit attached below, mostly written
by Peter:
30f93abc6cb3 sched, numa, mm: Add the scanning page fault machinery
Thanks,
Ingo
--------------------->
>From 30f93abc6cb3fd387a134d6b94ff5ac396be1c88 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Date: Tue, 13 Nov 2012 12:58:32 +0100
Subject: [PATCH] sched, numa, mm: Add the scanning page fault machinery
Add the NUMA working set scanning/hinting page fault machinery,
with no policy yet.
[ The earliest versions had the mpol_misplaced() function from
Lee Schermerhorn - this was heavily modified later on. ]
Also-written-by: Lee Schermerhorn <lee.schermerhorn@xxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
[ split it out of the main policy patch - as suggested by Mel Gorman ]
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
include/linux/init_task.h | 8 +++
include/linux/mempolicy.h | 6 +-
include/linux/mm_types.h | 4 ++
include/linux/sched.h | 41 ++++++++++++--
init/Kconfig | 73 +++++++++++++++++++-----
kernel/sched/core.c | 15 +++++
kernel/sysctl.c | 31 ++++++++++-
mm/huge_memory.c | 1 +
mm/mempolicy.c | 137 ++++++++++++++++++++++++++++++++++++++++++++++
9 files changed, 294 insertions(+), 22 deletions(-)
[...]
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index d04a8a5..318043a 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2175,6 +2175,143 @@ static void sp_free(struct sp_node *n)
kmem_cache_free(sn_cache, n);
}
+/*
+ * Multi-stage node selection is used in conjunction with a periodic
+ * migration fault to build a temporal task<->page relation. By
+ * using a two-stage filter we remove short/unlikely relations.
+ *
+ * Using P(p) ~ n_p / n_t as per frequentist probability, we can
+ * equate a task's usage of a particular page (n_p) per total usage
+ * of this page (n_t) (in a given time-span) to a probability.
+ *
+ * Our periodic faults will then sample this probability and getting
+ * the same result twice in a row, given these samples are fully
+ * independent, is then given by P(n)^2, provided our sample period
+ * is sufficiently short compared to the usage pattern.
+ *
+ * This quadric squishes small probabilities, making it less likely
+ * we act on an unlikely task<->page relation.
+ *
+ * Return the best node ID this page should be on, or -1 if it should
+ * stay where it is.
+ */
+static int
+numa_migration_target(struct page *page, int page_nid,
+ struct task_struct *p, int this_cpu,
+ int cpu_last_access)
+{
+ int nid_last_access;
+ int this_nid;
+
+ if (task_numa_shared(p) < 0)
+ return -1;
+
+ /*
+ * Possibly migrate towards the current node, depends on
+ * task_numa_placement() and access details.
+ */
+ nid_last_access = cpu_to_node(cpu_last_access);
+ this_nid = cpu_to_node(this_cpu);
+
+ if (nid_last_access != this_nid) {
+ /*
+ * 'Access miss': the page got last accessed from a remote node.
+ */
+ return -1;
+ }
+ /*
+ * 'Access hit': the page got last accessed from our node.
+ *
+ * Migrate the page if needed.
+ */
+
+ /* The page is already on this node: */
+ if (page_nid == this_nid)
+ return -1;
+
+ return this_nid;
+}
[...]
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