Hey, This should probably have a Co-developed-by: Tejun Heo <[email protected]>
I need to take a closer look at patch 4 and 6, to add my r-b over the rest. Den 2026-03-02 kl. 13:37, skrev Natalie Vock: > This helps to find a common subtree of two resources, which is important > when determining whether it's helpful to evict one resource in favor of > another. > > To facilitate this, add a common helper to find the ancestor of two > cgroups using each cgroup's ancestor array. > > Signed-off-by: Natalie Vock <[email protected]> > --- > include/linux/cgroup.h | 21 +++++++++++++++++++++ > include/linux/cgroup_dmem.h | 9 +++++++++ > kernel/cgroup/dmem.c | 43 ++++++++++++++++++++++++++++++++++++++++--- > 3 files changed, 70 insertions(+), 3 deletions(-) > > diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h > index bc892e3b37eea..560ae995e3a54 100644 > --- a/include/linux/cgroup.h > +++ b/include/linux/cgroup.h > @@ -561,6 +561,27 @@ static inline struct cgroup *cgroup_ancestor(struct > cgroup *cgrp, > return cgrp->ancestors[ancestor_level]; > } > > +/** > + * cgroup_common_ancestor - find common ancestor of two cgroups > + * @a: first cgroup to find common ancestor of > + * @b: second cgroup to find common ancestor of > + * > + * Find the first cgroup that is an ancestor of both @a and @b, if it exists > + * and return a pointer to it. If such a cgroup doesn't exist, return NULL. > + * > + * This function is safe to call as long as both @a and @b are accessible. > + */ > +static inline struct cgroup *cgroup_common_ancestor(struct cgroup *a, > + struct cgroup *b) > +{ > + int level; > + > + for (level = min(a->level, b->level); level >= 0; level--) > + if (a->ancestors[level] == b->ancestors[level]) > + return a->ancestors[level]; > + return NULL; > +} > + > /** > * task_under_cgroup_hierarchy - test task's membership of cgroup ancestry > * @task: the task to be tested > diff --git a/include/linux/cgroup_dmem.h b/include/linux/cgroup_dmem.h > index 1a88cd0c9eb00..444b84f4c253a 100644 > --- a/include/linux/cgroup_dmem.h > +++ b/include/linux/cgroup_dmem.h > @@ -28,6 +28,8 @@ bool dmem_cgroup_below_min(struct dmem_cgroup_pool_state > *root, > struct dmem_cgroup_pool_state *test); > bool dmem_cgroup_below_low(struct dmem_cgroup_pool_state *root, > struct dmem_cgroup_pool_state *test); > +struct dmem_cgroup_pool_state *dmem_cgroup_common_ancestor(struct > dmem_cgroup_pool_state *a, > + struct > dmem_cgroup_pool_state *b); > > void dmem_cgroup_pool_state_put(struct dmem_cgroup_pool_state *pool); > #else > @@ -75,6 +77,13 @@ static inline bool dmem_cgroup_below_low(struct > dmem_cgroup_pool_state *root, > return false; > } > > +static inline > +struct dmem_cgroup_pool_state *dmem_cgroup_common_ancestor(struct > dmem_cgroup_pool_state *a, > + struct > dmem_cgroup_pool_state *b) > +{ > + return NULL; > +} > + > static inline void dmem_cgroup_pool_state_put(struct dmem_cgroup_pool_state > *pool) > { } > > diff --git a/kernel/cgroup/dmem.c b/kernel/cgroup/dmem.c > index 28227405f7cfe..a3ba865f4c68f 100644 > --- a/kernel/cgroup/dmem.c > +++ b/kernel/cgroup/dmem.c > @@ -569,11 +569,10 @@ void dmem_cgroup_pool_state_put(struct > dmem_cgroup_pool_state *pool) > EXPORT_SYMBOL_GPL(dmem_cgroup_pool_state_put); > > static struct dmem_cgroup_pool_state * > -get_cg_pool_unlocked(struct dmemcg_state *cg, struct dmem_cgroup_region > *region) > +find_cg_pool_unlocked(struct dmemcg_state *cg, struct dmem_cgroup_region > *region) > { > - struct dmem_cgroup_pool_state *pool, *allocpool = NULL; > + struct dmem_cgroup_pool_state *pool; > > - /* fastpath lookup? */ > rcu_read_lock(); > pool = find_cg_pool_locked(cg, region); > if (pool && !READ_ONCE(pool->inited)) > @@ -582,6 +581,17 @@ get_cg_pool_unlocked(struct dmemcg_state *cg, struct > dmem_cgroup_region *region) > pool = NULL; > rcu_read_unlock(); > > + return pool; > +} > + > +static struct dmem_cgroup_pool_state * > +get_cg_pool_unlocked(struct dmemcg_state *cg, struct dmem_cgroup_region > *region) > +{ > + struct dmem_cgroup_pool_state *pool, *allocpool = NULL; > + > + /* fastpath lookup? */ > + pool = find_cg_pool_unlocked(cg, region); > + > while (!pool) { > spin_lock(&dmemcg_lock); > if (!region->unregistered) > @@ -756,6 +766,33 @@ bool dmem_cgroup_below_low(struct dmem_cgroup_pool_state > *root, > } > EXPORT_SYMBOL_GPL(dmem_cgroup_below_low); > > +/** > + * dmem_cgroup_common_ancestor(): Find the first common ancestor of two > pools. > + * @a: First pool to find the common ancestor of. > + * @b: First pool to find the common ancestor of. > + * > + * Return: The first pool that is a parent of both @a and @b, or NULL if > either @a or @b are NULL, > + * or if such a pool does not exist. > + */ > +struct dmem_cgroup_pool_state *dmem_cgroup_common_ancestor(struct > dmem_cgroup_pool_state *a, > + struct > dmem_cgroup_pool_state *b) > +{ > + struct cgroup *ancestor_cgroup; > + struct cgroup_subsys_state *ancestor_css; > + > + if (!a || !b) > + return NULL; > + > + ancestor_cgroup = cgroup_common_ancestor(a->cs->css.cgroup, > b->cs->css.cgroup); > + if (!ancestor_cgroup) > + return NULL; > + > + ancestor_css = cgroup_e_css(ancestor_cgroup, &dmem_cgrp_subsys); > + > + return find_cg_pool_unlocked(css_to_dmemcs(ancestor_css), a->region); > +} > +EXPORT_SYMBOL_GPL(dmem_cgroup_common_ancestor); >From the naming, I would not expect a reference to be taken to the common >ancestor, especially because the reference through a and b would both be able >keep the ancestor alive. Otherwise it would not be an ancestor. Rename to >dmem_cgroup_get_common_ancestor perhaps? Same for the find_, perhaps rename to >lookup_ or use the unmodified get_cg_pool_unlocked version, because the common >ancestor's pool_state definitely exists if either a or b do. Kind regards, ~Maarten Lankhorst
