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-rw-r--r--block/cfq-iosched.c19
1 files changed, 18 insertions, 1 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 98569c2f373e..e3c591dd8f19 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -632,6 +632,13 @@ static inline struct cfq_group *cfqg_parent(struct cfq_group *cfqg)
return pblkg ? blkg_to_cfqg(pblkg) : NULL;
}
+static inline bool cfqg_is_descendant(struct cfq_group *cfqg,
+ struct cfq_group *ancestor)
+{
+ return cgroup_is_descendant(cfqg_to_blkg(cfqg)->blkcg->css.cgroup,
+ cfqg_to_blkg(ancestor)->blkcg->css.cgroup);
+}
+
static inline void cfqg_get(struct cfq_group *cfqg)
{
return blkg_get(cfqg_to_blkg(cfqg));
@@ -758,6 +765,11 @@ static void cfqg_stats_xfer_dead(struct cfq_group *cfqg)
#else /* CONFIG_CFQ_GROUP_IOSCHED */
static inline struct cfq_group *cfqg_parent(struct cfq_group *cfqg) { return NULL; }
+static inline bool cfqg_is_descendant(struct cfq_group *cfqg,
+ struct cfq_group *ancestor)
+{
+ return true;
+}
static inline void cfqg_get(struct cfq_group *cfqg) { }
static inline void cfqg_put(struct cfq_group *cfqg) { }
@@ -3953,7 +3965,12 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
if (rq_is_sync(rq) && !cfq_cfqq_sync(cfqq))
return true;
- if (new_cfqq->cfqg != cfqq->cfqg)
+ /*
+ * Treat ancestors of current cgroup the same way as current cgroup.
+ * For anybody else we disallow preemption to guarantee service
+ * fairness among cgroups.
+ */
+ if (!cfqg_is_descendant(cfqq->cfqg, new_cfqq->cfqg))
return false;
if (cfq_slice_used(cfqq))
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