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Subject[Experimental][PATCH 21/21] memcg-new-hierarchical-reclaim.patch
Implement hierarchy reclaim by cgroup_id.

What changes:
- reclaim is not done by tree-walk algorithm
- mem_cgroup->last_schan_child is ID, not pointer.
- no cgroup_lock.
- scanning order is just defined by ID's order.
(Scan by round-robin logic.)

Changelog: v1 -> v2
- make use of css_tryget();
- count # of loops rather than remembering position.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujisu.com>


mm/memcontrol.c | 214 +++++++++++++++++++-------------------------------------
1 file changed, 75 insertions(+), 139 deletions(-)

Index: mmotm-2.6.28-Dec02/mm/memcontrol.c
===================================================================
--- mmotm-2.6.28-Dec02.orig/mm/memcontrol.c
+++ mmotm-2.6.28-Dec02/mm/memcontrol.c
@@ -153,9 +153,10 @@ struct mem_cgroup {

/*
* While reclaiming in a hiearchy, we cache the last child we
- * reclaimed from. Protected by cgroup_lock()
+ * reclaimed from.
*/
- struct mem_cgroup *last_scanned_child;
+ int last_scanned_child;
+ unsigned long scan_age;
/*
* Should the accounting and control be hierarchical, per subtree?
*/
@@ -521,108 +522,72 @@ unsigned long mem_cgroup_isolate_pages(u
return nr_taken;
}

-#define mem_cgroup_from_res_counter(counter, member) \
- container_of(counter, struct mem_cgroup, member)
-
-/*
- * This routine finds the DFS walk successor. This routine should be
- * called with cgroup_mutex held
- */
-static struct mem_cgroup *
-mem_cgroup_get_next_node(struct mem_cgroup *curr, struct mem_cgroup *root_mem)
+static unsigned int get_swappiness(struct mem_cgroup *memcg)
{
- struct cgroup *cgroup, *curr_cgroup, *root_cgroup;
-
- curr_cgroup = curr->css.cgroup;
- root_cgroup = root_mem->css.cgroup;
-
- if (!list_empty(&curr_cgroup->children)) {
- /*
- * Walk down to children
- */
- mem_cgroup_put(curr);
- cgroup = list_entry(curr_cgroup->children.next,
- struct cgroup, sibling);
- curr = mem_cgroup_from_cont(cgroup);
- mem_cgroup_get(curr);
- goto done;
- }
-
-visit_parent:
- if (curr_cgroup == root_cgroup) {
- mem_cgroup_put(curr);
- curr = root_mem;
- mem_cgroup_get(curr);
- goto done;
- }
+ struct cgroup *cgrp = memcg->css.cgroup;
+ unsigned int swappiness;

- /*
- * Goto next sibling
- */
- if (curr_cgroup->sibling.next != &curr_cgroup->parent->children) {
- mem_cgroup_put(curr);
- cgroup = list_entry(curr_cgroup->sibling.next, struct cgroup,
- sibling);
- curr = mem_cgroup_from_cont(cgroup);
- mem_cgroup_get(curr);
- goto done;
- }
+ /* root ? */
+ if (cgrp->parent == NULL)
+ return vm_swappiness;

- /*
- * Go up to next parent and next parent's sibling if need be
- */
- curr_cgroup = curr_cgroup->parent;
- goto visit_parent;
+ spin_lock(&memcg->reclaim_param_lock);
+ swappiness = memcg->swappiness;
+ spin_unlock(&memcg->reclaim_param_lock);

-done:
- root_mem->last_scanned_child = curr;
- return curr;
+ return swappiness;
}

+#define mem_cgroup_from_res_counter(counter, member) \
+ container_of(counter, struct mem_cgroup, member)
+
/*
- * Visit the first child (need not be the first child as per the ordering
- * of the cgroup list, since we track last_scanned_child) of @mem and use
- * that to reclaim free pages from.
+ * This routine select next memcg by ID. Using RCU and tryget().
+ * No cgroup_mutex is required.
*/
static struct mem_cgroup *
-mem_cgroup_get_first_node(struct mem_cgroup *root_mem)
+mem_cgroup_select_victim(struct mem_cgroup *root_mem)
{
- struct cgroup *cgroup;
+ struct cgroup *cgroup, *root_cgroup;
struct mem_cgroup *ret;
- struct mem_cgroup *last_scan = root_mem->last_scanned_child;
- bool obsolete = false;
+ int nextid, rootid, depth, found;

- if (last_scan) {
- if (css_under_removal(&last_scan->css))
- obsolete = true;
- } else
- obsolete = true;
+ root_cgroup = root_mem->css.cgroup;
+ rootid = cgroup_id(root_cgroup);
+ depth = cgroup_depth(root_cgroup);
+ found = 0;
+ ret = NULL;

- /*
- * Scan all children under the mem_cgroup mem
- */
- cgroup_lock();
- if (list_empty(&root_mem->css.cgroup->children)) {
- ret = root_mem;
- goto done;
+ rcu_read_lock();
+ if (!root_mem->use_hierarchy) {
+ spin_lock(&root_mem->reclaim_param_lock);
+ root_mem->scan_age++;
+ spin_unlock(&root_mem->reclaim_param_lock);
+ css_get(&root_mem->css);
+ goto out;
}

- if (!root_mem->last_scanned_child || obsolete) {
-
- if (obsolete)
- mem_cgroup_put(root_mem->last_scanned_child);
-
- cgroup = list_first_entry(&root_mem->css.cgroup->children,
- struct cgroup, sibling);
- ret = mem_cgroup_from_cont(cgroup);
- mem_cgroup_get(ret);
- } else
- ret = mem_cgroup_get_next_node(root_mem->last_scanned_child,
- root_mem);
+ while (!ret) {
+ /* ID:0 is not used by cgroup-id */
+ nextid = root_mem->last_scanned_child + 1;
+ cgroup = cgroup_get_next(nextid, rootid, depth, &found);
+ if (cgroup) {
+ spin_lock(&root_mem->reclaim_param_lock);
+ root_mem->last_scanned_child = found;
+ spin_unlock(&root_mem->reclaim_param_lock);
+ ret = mem_cgroup_from_cont(cgroup);
+ if (!css_tryget(&ret->css))
+ ret = NULL;
+ } else {
+ spin_lock(&root_mem->reclaim_param_lock);
+ root_mem->scan_age++;
+ root_mem->last_scanned_child = 0;
+ spin_unlock(&root_mem->reclaim_param_lock);
+ }
+ }
+out:
+ rcu_read_unlock();

-done:
- root_mem->last_scanned_child = ret;
- cgroup_unlock();
return ret;
}

@@ -638,67 +603,34 @@ static bool mem_cgroup_check_under_limit
return false;
}

-static unsigned int get_swappiness(struct mem_cgroup *memcg)
-{
- struct cgroup *cgrp = memcg->css.cgroup;
- unsigned int swappiness;
-
- /* root ? */
- if (cgrp->parent == NULL)
- return vm_swappiness;
-
- spin_lock(&memcg->reclaim_param_lock);
- swappiness = memcg->swappiness;
- spin_unlock(&memcg->reclaim_param_lock);
-
- return swappiness;
-}

/*
- * Dance down the hierarchy if needed to reclaim memory. We remember the
- * last child we reclaimed from, so that we don't end up penalizing
- * one child extensively based on its position in the children list.
- *
* root_mem is the original ancestor that we've been reclaim from.
*/
static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
gfp_t gfp_mask, bool noswap)
{
- struct mem_cgroup *next_mem;
+ struct mem_cgroup *victim;
+ unsigned long start_age;
int ret = 0;
+ int total = 0;

- /*
- * Reclaim unconditionally and don't check for return value.
- * We need to reclaim in the current group and down the tree.
- * One might think about checking for children before reclaiming,
- * but there might be left over accounting, even after children
- * have left.
- */
- ret = try_to_free_mem_cgroup_pages(root_mem, gfp_mask, noswap,
- get_swappiness(root_mem));
- if (mem_cgroup_check_under_limit(root_mem))
- return 0;
- if (!root_mem->use_hierarchy)
- return ret;
-
- next_mem = mem_cgroup_get_first_node(root_mem);
-
- while (next_mem != root_mem) {
- if (css_under_removal(&next_mem->css)) {
- mem_cgroup_put(next_mem);
- cgroup_lock();
- next_mem = mem_cgroup_get_first_node(root_mem);
- cgroup_unlock();
- continue;
- }
- ret = try_to_free_mem_cgroup_pages(next_mem, gfp_mask, noswap,
- get_swappiness(next_mem));
+ start_age = root_mem->scan_age;
+ /* allows 2 times of loops */
+ while (time_after((start_age + 2UL), root_mem->scan_age)) {
+ victim = mem_cgroup_select_victim(root_mem);
+ ret = try_to_free_mem_cgroup_pages(victim,
+ gfp_mask, noswap, get_swappiness(victim));
+ css_put(&victim->css);
if (mem_cgroup_check_under_limit(root_mem))
- return 0;
- cgroup_lock();
- next_mem = mem_cgroup_get_next_node(next_mem, root_mem);
- cgroup_unlock();
+ return 1;
+ total += ret;
}
+
+ ret = total;
+ if (mem_cgroup_check_under_limit(root_mem))
+ ret = 1;
+
return ret;
}

@@ -787,6 +719,8 @@ static int __mem_cgroup_try_charge(struc

ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, gfp_mask,
noswap);
+ if (ret)
+ continue;

/*
* try_to_free_mem_cgroup_pages() might not give us a full
@@ -2161,7 +2095,8 @@ mem_cgroup_create(struct cgroup_subsys *
res_counter_init(&mem->memsw, NULL);
}
mem_cgroup_set_inactive_ratio(mem);
- mem->last_scanned_child = NULL;
+ mem->last_scanned_child = 0;
+ mem->scan_age = 0;
spin_lock_init(&mem->reclaim_param_lock);

if (parent)


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