sched/numa: Do not trap hinting faults for shared libraries

NUMA hinting faults will not migrate a shared executable page mapped by
multiple processes on the grounds that the data is probably in the CPU
cache already and the page may just bounce between tasks running on multipl
nodes. Even if the migration is avoided, there is still the overhead of
trapping the fault, updating the statistics, making scheduler placement
decisions based on the information etc. If we are never going to migrate
the page, it is overhead for no gain and worse a process may be placed on
a sub-optimal node for shared executable pages. This patch avoids trapping
faults for shared libraries entirely.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-36-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index de9b4d8eb853bd2230488a1601608d487812c195..fbc0c84a8a043b4e6ad6a4ae97d2b106a22c6c81 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1231,6 +1231,16 @@ void task_numa_work(struct callback_head *work)
                if (!vma_migratable(vma) || !vma_policy_mof(p, vma))
                        continue;
 
+               /*
+                * Shared library pages mapped by multiple processes are not
+                * migrated as it is expected they are cache replicated. Avoid
+                * hinting faults in read-only file-backed mappings or the vdso
+                * as migrating the pages will be of marginal benefit.
+                */
+               if (!vma->vm_mm ||
+                   (vma->vm_file && (vma->vm_flags & (VM_READ|VM_WRITE)) == (VM_READ)))
+                       continue;
+
                do {
                        start = max(start, vma->vm_start);
                        end = ALIGN(start + (pages << PAGE_SHIFT), HPAGE_SIZE);