The current implementation of softlimit is based on per-zone RB tree, where
only the cgroup exceeds the soft_limit the most being selected for reclaim.
The problems are:
1. It takes no consideration of how many pages actually allocated on the zone
from this cgroup. The RB tree is indexed by the cgroup_(usage - soft_limit).
2. It makes less sense to only reclaim from one cgroup rather than reclaiming
all cgroups based on calculated propotion. This is required for fairness.
3. The target of the soft limit reclaim is to bring one cgroup's usage under
its soft_limit. However the target of global memory pressure is to reclaim
pages above the zone's high_wmark.
So the current softlimit reclaim is far from fulfilling the efficiency
requirement. From the discussion on LSF mm session, we agree to change to
organizing the memcgs in a round-robin fashion. This patch is to revert the
current RB-Tree implementation.
Signed-off-by: Ying Han <yinghan@xxxxxxxxxx>
---
mm/memcontrol.c | 304 +------------------------------------------------------
1 files changed, 1 insertions(+), 303 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index da1fb2b..9da3ecf 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -34,7 +34,6 @@
#include <linux/rcupdate.h>
#include <linux/limits.h>
#include <linux/mutex.h>
-#include <linux/rbtree.h>
#include <linux/slab.h>
#include <linux/swap.h>
#include <linux/swapops.h>
@@ -137,10 +136,6 @@ struct mem_cgroup_per_zone {
unsigned long count[NR_LRU_LISTS];
struct zone_reclaim_stat reclaim_stat;
- struct rb_node tree_node; /* RB tree node */
- unsigned long long usage_in_excess;/* Set to the value by which */
- /* the soft limit is exceeded*/
- bool on_tree;
struct mem_cgroup *mem; /* Back pointer, we cannot */
/* use container_of */
};
@@ -155,26 +150,6 @@ struct mem_cgroup_lru_info {
struct mem_cgroup_per_node *nodeinfo[MAX_NUMNODES];
};
-/*
- * Cgroups above their limits are maintained in a RB-Tree, independent of
- * their hierarchy representation
- */
-
-struct mem_cgroup_tree_per_zone {
- struct rb_root rb_root;
- spinlock_t lock;
-};
-
-struct mem_cgroup_tree_per_node {
- struct mem_cgroup_tree_per_zone rb_tree_per_zone[MAX_NR_ZONES];
-};
-
-struct mem_cgroup_tree {
- struct mem_cgroup_tree_per_node *rb_tree_per_node[MAX_NUMNODES];
-};
-
-static struct mem_cgroup_tree soft_limit_tree __read_mostly;
-
struct mem_cgroup_threshold {
struct eventfd_ctx *eventfd;
u64 threshold;
@@ -384,164 +359,6 @@ page_cgroup_zoneinfo(struct mem_cgroup *mem, struct page *page)
return mem_cgroup_zoneinfo(mem, nid, zid);
}
-static struct mem_cgroup_tree_per_zone *
-soft_limit_tree_node_zone(int nid, int zid)
-{
- return &soft_limit_tree.rb_tree_per_node[nid]->rb_tree_per_zone[zid];
-}
-
-static struct mem_cgroup_tree_per_zone *
-soft_limit_tree_from_page(struct page *page)
-{
- int nid = page_to_nid(page);
- int zid = page_zonenum(page);
-
- return &soft_limit_tree.rb_tree_per_node[nid]->rb_tree_per_zone[zid];
-}
-
-static void
-__mem_cgroup_insert_exceeded(struct mem_cgroup *mem,
- struct mem_cgroup_per_zone *mz,
- struct mem_cgroup_tree_per_zone *mctz,
- unsigned long long new_usage_in_excess)
-{
- struct rb_node **p = &mctz->rb_root.rb_node;
- struct rb_node *parent = NULL;
- struct mem_cgroup_per_zone *mz_node;
-
- if (mz->on_tree)
- return;
-
- mz->usage_in_excess = new_usage_in_excess;
- if (!mz->usage_in_excess)
- return;
- while (*p) {
- parent = *p;
- mz_node = rb_entry(parent, struct mem_cgroup_per_zone,
- tree_node);
- if (mz->usage_in_excess < mz_node->usage_in_excess)
- p = &(*p)->rb_left;
- /*
- * We can't avoid mem cgroups that are over their soft
- * limit by the same amount
- */
- else if (mz->usage_in_excess >= mz_node->usage_in_excess)
- p = &(*p)->rb_right;
- }
- rb_link_node(&mz->tree_node, parent, p);
- rb_insert_color(&mz->tree_node, &mctz->rb_root);
- mz->on_tree = true;
-}
-
-static void
-__mem_cgroup_remove_exceeded(struct mem_cgroup *mem,
- struct mem_cgroup_per_zone *mz,
- struct mem_cgroup_tree_per_zone *mctz)
-{
- if (!mz->on_tree)
- return;
- rb_erase(&mz->tree_node, &mctz->rb_root);
- mz->on_tree = false;
-}
-
-static void
-mem_cgroup_remove_exceeded(struct mem_cgroup *mem,
- struct mem_cgroup_per_zone *mz,
- struct mem_cgroup_tree_per_zone *mctz)
-{
- spin_lock(&mctz->lock);
- __mem_cgroup_remove_exceeded(mem, mz, mctz);
- spin_unlock(&mctz->lock);
-}
-
-
-static void mem_cgroup_update_tree(struct mem_cgroup *mem, struct page *page)
-{
- unsigned long long excess;
- struct mem_cgroup_per_zone *mz;
- struct mem_cgroup_tree_per_zone *mctz;
- int nid = page_to_nid(page);
- int zid = page_zonenum(page);
- mctz = soft_limit_tree_from_page(page);
-
- /*
- * Necessary to update all ancestors when hierarchy is used.
- * because their event counter is not touched.
- */
- for (; mem; mem = parent_mem_cgroup(mem)) {
- mz = mem_cgroup_zoneinfo(mem, nid, zid);
- excess = res_counter_soft_limit_excess(&mem->res);
- /*
- * We have to update the tree if mz is on RB-tree or
- * mem is over its softlimit.
- */
- if (excess || mz->on_tree) {
- spin_lock(&mctz->lock);
- /* if on-tree, remove it */
- if (mz->on_tree)
- __mem_cgroup_remove_exceeded(mem, mz, mctz);
- /*
- * Insert again. mz->usage_in_excess will be updated.
- * If excess is 0, no tree ops.
- */
- __mem_cgroup_insert_exceeded(mem, mz, mctz, excess);
- spin_unlock(&mctz->lock);
- }
- }
-}
-
-static void mem_cgroup_remove_from_trees(struct mem_cgroup *mem)
-{
- int node, zone;
- struct mem_cgroup_per_zone *mz;
- struct mem_cgroup_tree_per_zone *mctz;
-
- for_each_node_state(node, N_POSSIBLE) {
- for (zone = 0; zone < MAX_NR_ZONES; zone++) {
- mz = mem_cgroup_zoneinfo(mem, node, zone);
- mctz = soft_limit_tree_node_zone(node, zone);
- mem_cgroup_remove_exceeded(mem, mz, mctz);
- }
- }
-}
-
-static struct mem_cgroup_per_zone *
-__mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz)
-{
- struct rb_node *rightmost = NULL;
- struct mem_cgroup_per_zone *mz;
-
-retry:
- mz = NULL;
- rightmost = rb_last(&mctz->rb_root);
- if (!rightmost)
- goto done; /* Nothing to reclaim from */
-
- mz = rb_entry(rightmost, struct mem_cgroup_per_zone, tree_node);
- /*
- * Remove the node now but someone else can add it back,
- * we will to add it back at the end of reclaim to its correct
- * position in the tree.
- */
- __mem_cgroup_remove_exceeded(mz->mem, mz, mctz);
- if (!res_counter_soft_limit_excess(&mz->mem->res) ||
- !css_tryget(&mz->mem->css))
- goto retry;
-done:
- return mz;
-}
-
-static struct mem_cgroup_per_zone *
-mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz)
-{
- struct mem_cgroup_per_zone *mz;
-
- spin_lock(&mctz->lock);
- mz = __mem_cgroup_largest_soft_limit_node(mctz);
- spin_unlock(&mctz->lock);
- return mz;
-}
-
/*
* Implementation Note: reading percpu statistics for memcg.
*
@@ -727,7 +544,6 @@ static void memcg_check_events(struct mem_cgroup *mem, struct page *page)
__mem_cgroup_target_update(mem, MEM_CGROUP_TARGET_THRESH);
if (unlikely(__memcg_event_check(mem,
MEM_CGROUP_TARGET_SOFTLIMIT))){
- mem_cgroup_update_tree(mem, page);
__mem_cgroup_target_update(mem,
MEM_CGROUP_TARGET_SOFTLIMIT);
}
@@ -3373,95 +3189,7 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
gfp_t gfp_mask,
unsigned long *total_scanned)
{
- unsigned long nr_reclaimed = 0;
- struct mem_cgroup_per_zone *mz, *next_mz = NULL;
- unsigned long reclaimed;
- int loop = 0;
- struct mem_cgroup_tree_per_zone *mctz;
- unsigned long long excess;
- unsigned long nr_scanned;
-
- if (order > 0)
- return 0;
-
- mctz = soft_limit_tree_node_zone(zone_to_nid(zone), zone_idx(zone));
- /*
- * This loop can run a while, specially if mem_cgroup's continuously
- * keep exceeding their soft limit and putting the system under
- * pressure
- */
- do {
- if (next_mz)
- mz = next_mz;
- else
- mz = mem_cgroup_largest_soft_limit_node(mctz);
- if (!mz)
- break;
-
- nr_scanned = 0;
- reclaimed = mem_cgroup_hierarchical_reclaim(mz->mem, zone,
- gfp_mask,
- MEM_CGROUP_RECLAIM_SOFT,
- &nr_scanned);
- nr_reclaimed += reclaimed;
- *total_scanned += nr_scanned;
-
- spin_lock(&mctz->lock);
-
- /*
- * If we failed to reclaim anything from this memory cgroup
- * it is time to move on to the next cgroup
- */
- next_mz = NULL;
- if (!reclaimed) {
- do {
- /*
- * Loop until we find yet another one.
- *
- * By the time we get the soft_limit lock
- * again, someone might have aded the
- * group back on the RB tree. Iterate to
- * make sure we get a different mem.
- * mem_cgroup_largest_soft_limit_node returns
- * NULL if no other cgroup is present on
- * the tree
- */
- next_mz =
- __mem_cgroup_largest_soft_limit_node(mctz);
- if (next_mz == mz)
- css_put(&next_mz->mem->css);
- else /* next_mz == NULL or other memcg */
- break;
- } while (1);
- }
- __mem_cgroup_remove_exceeded(mz->mem, mz, mctz);
- excess = res_counter_soft_limit_excess(&mz->mem->res);
- /*
- * One school of thought says that we should not add
- * back the node to the tree if reclaim returns 0.
- * But our reclaim could return 0, simply because due
- * to priority we are exposing a smaller subset of
- * memory to reclaim from. Consider this as a longer
- * term TODO.
- */
- /* If excess == 0, no tree ops */
- __mem_cgroup_insert_exceeded(mz->mem, mz, mctz, excess);
- spin_unlock(&mctz->lock);
- css_put(&mz->mem->css);
- loop++;
- /*
- * Could not reclaim anything and there are no more
- * mem cgroups to try or we seem to be looping without
- * reclaiming anything.
- */
- if (!nr_reclaimed &&
- (next_mz == NULL ||
- loop > MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS))
- break;
- } while (!nr_reclaimed);
- if (next_mz)
- css_put(&next_mz->mem->css);
- return nr_reclaimed;
+ return 0;
}
/*
@@ -4525,8 +4253,6 @@ static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
mz = &pn->zoneinfo[zone];
for_each_lru(l)
INIT_LIST_HEAD(&mz->lists[l]);
- mz->usage_in_excess = 0;
- mz->on_tree = false;
mz->mem = mem;
}
return 0;
@@ -4580,7 +4306,6 @@ static void __mem_cgroup_free(struct mem_cgroup *mem)
{
int node;
- mem_cgroup_remove_from_trees(mem);
free_css_id(&mem_cgroup_subsys, &mem->css);
for_each_node_state(node, N_POSSIBLE)
@@ -4635,31 +4360,6 @@ static void __init enable_swap_cgroup(void)
}
#endif
-static int mem_cgroup_soft_limit_tree_init(void)
-{
- struct mem_cgroup_tree_per_node *rtpn;
- struct mem_cgroup_tree_per_zone *rtpz;
- int tmp, node, zone;
-
- for_each_node_state(node, N_POSSIBLE) {
- tmp = node;
- if (!node_state(node, N_NORMAL_MEMORY))
- tmp = -1;
- rtpn = kzalloc_node(sizeof(*rtpn), GFP_KERNEL, tmp);
- if (!rtpn)
- return 1;
-
- soft_limit_tree.rb_tree_per_node[node] = rtpn;
-
- for (zone = 0; zone < MAX_NR_ZONES; zone++) {
- rtpz = &rtpn->rb_tree_per_zone[zone];
- rtpz->rb_root = RB_ROOT;
- spin_lock_init(&rtpz->lock);
- }
- }
- return 0;
-}
-
static struct cgroup_subsys_state * __ref
mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
{
@@ -4681,8 +4381,6 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
enable_swap_cgroup();
parent = NULL;
root_mem_cgroup = mem;
- if (mem_cgroup_soft_limit_tree_init())
- goto free_out;
for_each_possible_cpu(cpu) {
struct memcg_stock_pcp *stock =
&per_cpu(memcg_stock, cpu);
--
1.7.3.1
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