Messages in this thread | | | Date | Fri, 9 Jan 2009 11:03:23 +0530 | From | Balbir Singh <> | Subject | Re: [RFC][PATCH 3/4] memcg: fix for mem_cgroup_hierarchical_reclaim |
| |
* Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> [2009-01-08 19:15:01]:
> If root_mem has no children, last_scaned_child is set to root_mem itself. > But after some children added to root_mem, mem_cgroup_get_next_node can > mem_cgroup_put the root_mem although root_mem has not been mem_cgroup_get. >
Good catch!
> This patch fixes this behavior by: > - Set last_scanned_child to NULL if root_mem has no children or DFS search > has returned to root_mem itself(root_mem is not a "child" of root_mem). > Make mem_cgroup_get_first_node return root_mem in this case. > There are no mem_cgroup_get/put for root_mem. > - Rename mem_cgroup_get_next_node to __mem_cgroup_get_next_node, and > mem_cgroup_get_first_node to mem_cgroup_get_next_node. > Make mem_cgroup_hierarchical_reclaim call only new mem_cgroup_get_next_node. >
How have you tested these changes? When I wrote up the patches, I did several tests to make sure that all nodes in the hierarchy are covered while reclaiming in order.
> > Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> > --- > mm/memcontrol.c | 37 +++++++++++++++++++++---------------- > 1 files changed, 21 insertions(+), 16 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 288e22c..dc38a0e 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -622,7 +622,7 @@ unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan, > * called with hierarchy_mutex held > */ > static struct mem_cgroup * > -mem_cgroup_get_next_node(struct mem_cgroup *curr, struct mem_cgroup *root_mem) > +__mem_cgroup_get_next_node(struct mem_cgroup *curr, struct mem_cgroup *root_mem) > { > struct cgroup *cgroup, *curr_cgroup, *root_cgroup; > > @@ -644,8 +644,8 @@ mem_cgroup_get_next_node(struct mem_cgroup *curr, struct mem_cgroup *root_mem) > visit_parent: > if (curr_cgroup == root_cgroup) { > mem_cgroup_put(curr); > - curr = root_mem; > - mem_cgroup_get(curr); > + /* caller handles NULL case */ > + curr = NULL; > goto done; > } > > @@ -668,7 +668,6 @@ visit_parent: > goto visit_parent; > > done: > - root_mem->last_scanned_child = curr; > return curr; > } > > @@ -678,20 +677,29 @@ done: > * that to reclaim free pages from. > */ > static struct mem_cgroup * > -mem_cgroup_get_first_node(struct mem_cgroup *root_mem) > +mem_cgroup_get_next_node(struct mem_cgroup *root_mem) > { > struct cgroup *cgroup; > struct mem_cgroup *ret; > bool obsolete; > > - obsolete = mem_cgroup_is_obsolete(root_mem->last_scanned_child); > - > /* > * Scan all children under the mem_cgroup mem > */ > mutex_lock(&mem_cgroup_subsys.hierarchy_mutex); > + > + obsolete = mem_cgroup_is_obsolete(root_mem->last_scanned_child); > + > if (list_empty(&root_mem->css.cgroup->children)) { > - ret = root_mem; > + /* > + * root_mem might have children before and last_scanned_child > + * may point to one of them. > + */ > + if (root_mem->last_scanned_child) { > + VM_BUG_ON(!obsolete); > + mem_cgroup_put(root_mem->last_scanned_child); > + } > + ret = NULL; > goto done; > } > > @@ -705,13 +713,13 @@ mem_cgroup_get_first_node(struct mem_cgroup *root_mem) > ret = mem_cgroup_from_cont(cgroup); > mem_cgroup_get(ret); > } else > - ret = mem_cgroup_get_next_node(root_mem->last_scanned_child, > + ret = __mem_cgroup_get_next_node(root_mem->last_scanned_child, > root_mem); > > done: > root_mem->last_scanned_child = ret; > mutex_unlock(&mem_cgroup_subsys.hierarchy_mutex); > - return ret; > + return (ret) ? ret : root_mem; > } > > static bool mem_cgroup_check_under_limit(struct mem_cgroup *mem) > @@ -769,21 +777,18 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem, > if (!root_mem->use_hierarchy) > return ret; > > - next_mem = mem_cgroup_get_first_node(root_mem); > + next_mem = mem_cgroup_get_next_node(root_mem); > > while (next_mem != root_mem) { > if (mem_cgroup_is_obsolete(next_mem)) { > - mem_cgroup_put(next_mem); > - next_mem = mem_cgroup_get_first_node(root_mem); > + next_mem = mem_cgroup_get_next_node(root_mem); > continue; > } > ret = try_to_free_mem_cgroup_pages(next_mem, gfp_mask, noswap, > get_swappiness(next_mem)); > if (mem_cgroup_check_under_limit(root_mem)) > return 0; > - mutex_lock(&mem_cgroup_subsys.hierarchy_mutex); > - next_mem = mem_cgroup_get_next_node(next_mem, root_mem); > - mutex_unlock(&mem_cgroup_subsys.hierarchy_mutex); > + next_mem = mem_cgroup_get_next_node(root_mem); > } > return ret; > } >
Looks good to me, I need to test it though
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
-- Balbir
| |