diff options
| author | Mel Gorman <mgorman@suse.de> | 2012-11-12 09:17:07 +0000 |
|---|---|---|
| committer | Mel Gorman <mgorman@suse.de> | 2012-12-11 14:42:54 +0000 |
| commit | e42c8ff2999de1239a57d434bfbd8e9f2a56e814 (patch) | |
| tree | fd1975853a79bf28356d86a4822e8cd2111129a8 /mm/mempolicy.c | |
| parent | bac0382c6ad764156025978845147e5a6eccca09 (diff) | |
mm: numa: Use a two-stage filter to restrict pages being migrated for unlikely task<->node relationships
Note: This two-stage filter was taken directly from the sched/numa patch
"sched, numa, mm: Add the scanning page fault machinery" but is
only a partial extraction. As the end result is not necessarily
recognisable, the signed-offs-by had to be removed. Will be added
back if requested.
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@suse.de>
Diffstat (limited to 'mm/mempolicy.c')
| -rw-r--r-- | mm/mempolicy.c | 30 |
1 files changed, 29 insertions, 1 deletions
diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 4c1c8d83ac6..fd20e28fd2a 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: |