From: Kairui Song <kasong@xxxxxxxxxxx>
Currently, there is a lot of code for detecting reparent racing
using kmemcg_id as the synchronization flag. And an intermediate
table is required to record and compare the kmemcg_id.
We can simplify this by just checking the cgroup css status, skip
if cgroup is being offlined. On the reparenting side, ensure no
more allocation is on going and no further allocation will occur
by using the XArray lock as barrier.
Combined with a O(n^2) top-down walk for the allocation, we get rid
of the intermediate table allocation completely. Despite being O(n^2),
it should be actually faster because it's not practical to have a very
deep cgroup level.
This also avoided changing kmemcg_id before reparenting, making
cgroups have a stable index for list_lru_memcg. After this change
it's possible that a dying cgroup will see a NULL value in XArray
corresponding to the kmemcg_id, because the kmemcg_id will point
to an empty slot. In such case, just fallback to use its parent.
As a result the code is simpler, following test also showed a
performance gain (6 test runs):
mkdir /tmp/test-fs
modprobe brd rd_nr=1 rd_size=16777216
mkfs.xfs /dev/ram0
mount -t xfs /dev/ram0 /tmp/test-fs
worker() {
echo TEST-CONTENT > "/tmp/test-fs/$1"
}
do_test() {
for i in $(seq 1 2048); do
(exec sh -c 'echo "$PPID"') > "/sys/fs/cgroup/benchmark/$i/cgroup.procs"
worker "$i" &
done; wait
echo 1 > /proc/sys/vm/drop_caches
}
mkdir -p /sys/fs/cgroup/benchmark
echo +memory > /sys/fs/cgroup/benchmark/cgroup.subtree_control
for i in $(seq 1 2048); do
rmdir "/sys/fs/cgroup/benchmark/$i" &>/dev/null
mkdir -p "/sys/fs/cgroup/benchmark/$i"
done
time do_test
Before:
real 0m5.932s user 0m2.366s sys 0m5.583s
real 0m5.939s user 0m2.347s sys 0m5.597s
real 0m6.149s user 0m2.398s sys 0m5.761s
real 0m5.945s user 0m2.403s sys 0m5.547s
real 0m5.925s user 0m2.293s sys 0m5.651s
real 0m6.017s user 0m2.367s sys 0m5.686s
After:
real 0m5.712s user 0m2.343s sys 0m5.307s
real 0m5.885s user 0m2.326s sys 0m5.518s
real 0m5.694s user 0m2.347s sys 0m5.264s
real 0m5.865s user 0m2.300s sys 0m5.545s
real 0m5.748s user 0m2.273s sys 0m5.424s
real 0m5.756s user 0m2.318s sys 0m5.398s
Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
---
mm/list_lru.c | 182 ++++++++++++++++++++++----------------------------
mm/zswap.c | 7 +-
2 files changed, 81 insertions(+), 108 deletions(-)
diff --git a/mm/list_lru.c b/mm/list_lru.c
index 4c619857e916..ac8aec8451dd 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -59,6 +59,20 @@ list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
}
return &lru->node[nid].lru;
}
+
+static inline struct list_lru_one *
+list_lru_from_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg)
+{
+ struct list_lru_one *l;
+again:
+ l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
+ if (likely(l))
+ return l;
+
+ memcg = parent_mem_cgroup(memcg);
+ WARN_ON(!css_is_dying(&memcg->css));
+ goto again;
+}
#else
static void list_lru_register(struct list_lru *lru)
{
@@ -83,6 +97,12 @@ list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
{
return &lru->node[nid].lru;
}
+
+static inline struct list_lru_one *
+list_lru_from_memcg(struct list_lru *lru, int nid, int idx)
+{
+ return &lru->node[nid].lru;
+}
#endif /* CONFIG_MEMCG_KMEM */
bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid,
@@ -93,7 +113,7 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid,
spin_lock(&nlru->lock);
if (list_empty(item)) {
- l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
+ l = list_lru_from_memcg(lru, nid, memcg);
list_add_tail(item, &l->list);
/* Set shrinker bit if the first element was added */
if (!l->nr_items++)
@@ -124,7 +144,7 @@ bool list_lru_del(struct list_lru *lru, struct list_head *item, int nid,
spin_lock(&nlru->lock);
if (!list_empty(item)) {
- l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
+ l = list_lru_from_memcg(lru, nid, memcg);
list_del_init(item);
l->nr_items--;
nlru->nr_items--;
@@ -339,20 +359,6 @@ static struct list_lru_memcg *memcg_init_list_lru_one(gfp_t gfp)
return mlru;
}
-static void memcg_list_lru_free(struct list_lru *lru, int src_idx)
-{
- struct list_lru_memcg *mlru = xa_erase_irq(&lru->xa, src_idx);
-
- /*
- * The __list_lru_walk_one() can walk the list of this node.
- * We need kvfree_rcu() here. And the walking of the list
- * is under lru->node[nid]->lock, which can serve as a RCU
- * read-side critical section.
- */
- if (mlru)
- kvfree_rcu(mlru, rcu);
-}
-
static inline void memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
{
if (memcg_aware)
@@ -377,22 +383,18 @@ static void memcg_destroy_list_lru(struct list_lru *lru)
}
static void memcg_reparent_list_lru_node(struct list_lru *lru, int nid,
- int src_idx, struct mem_cgroup *dst_memcg)
+ struct list_lru_one *src,
+ struct mem_cgroup *dst_memcg)
{
struct list_lru_node *nlru = &lru->node[nid];
- int dst_idx = dst_memcg->kmemcg_id;
- struct list_lru_one *src, *dst;
+ struct list_lru_one *dst;
/*
* Since list_lru_{add,del} may be called under an IRQ-safe lock,
* we have to use IRQ-safe primitives here to avoid deadlock.
*/
spin_lock_irq(&nlru->lock);
-
- src = list_lru_from_memcg_idx(lru, nid, src_idx);
- if (!src)
- goto out;
- dst = list_lru_from_memcg_idx(lru, nid, dst_idx);
+ dst = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(dst_memcg));
list_splice_init(&src->list, &dst->list);
@@ -401,46 +403,45 @@ static void memcg_reparent_list_lru_node(struct list_lru *lru, int nid,
set_shrinker_bit(dst_memcg, nid, lru_shrinker_id(lru));
src->nr_items = 0;
}
-out:
spin_unlock_irq(&nlru->lock);
}
void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *parent)
{
- struct cgroup_subsys_state *css;
struct list_lru *lru;
- int src_idx = memcg->kmemcg_id, i;
-
- /*
- * Change kmemcg_id of this cgroup and all its descendants to the
- * parent's id, and then move all entries from this cgroup's list_lrus
- * to ones of the parent.
- */
- rcu_read_lock();
- css_for_each_descendant_pre(css, &memcg->css) {
- struct mem_cgroup *child;
-
- child = mem_cgroup_from_css(css);
- WRITE_ONCE(child->kmemcg_id, parent->kmemcg_id);
- }
- rcu_read_unlock();
+ int i;
- /*
- * With kmemcg_id set to parent, holding the lru lock below can
- * prevent list_lru_{add,del,isolate} from touching the lru, safe
- * to reparent.
- */
mutex_lock(&list_lrus_mutex);
list_for_each_entry(lru, &memcg_list_lrus, list) {
+ struct list_lru_memcg *mlru;
+ XA_STATE(xas, &lru->xa, memcg->kmemcg_id);
+
+ /*
+ * Lock the Xarray to ensure no on going allocation and
+ * further allocation will see css_is_dying().
+ */
+ xas_lock_irq(&xas);
+ mlru = xas_load(&xas);
+ if (mlru)
+ xas_store(&xas, NULL);
+ xas_unlock_irq(&xas);
+ if (!mlru)
+ continue;
+
+ /*
+ * With Xarray value set to NULL, holding the lru lock below
+ * prevents list_lru_{add,del,isolate} from touching the lru,
+ * safe to reparent.
+ */
for_each_node(i)
- memcg_reparent_list_lru_node(lru, i, src_idx, parent);
+ memcg_reparent_list_lru_node(lru, i, &mlru->node[i], parent);
/*
* Here all list_lrus corresponding to the cgroup are guaranteed
* to remain empty, we can safely free this lru, any further
* memcg_list_lru_alloc() call will simply bail out.
*/
- memcg_list_lru_free(lru, src_idx);
+ kvfree_rcu(mlru, rcu);
}
mutex_unlock(&list_lrus_mutex);
}
@@ -456,78 +457,51 @@ static inline bool memcg_list_lru_allocated(struct mem_cgroup *memcg,
int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
gfp_t gfp)
{
- int i;
unsigned long flags;
- struct list_lru_memcg_table {
- struct list_lru_memcg *mlru;
- struct mem_cgroup *memcg;
- } *table;
+ struct list_lru_memcg *mlru;
+ struct mem_cgroup *pos, *parent;
XA_STATE(xas, &lru->xa, 0);
if (!list_lru_memcg_aware(lru) || memcg_list_lru_allocated(memcg, lru))
return 0;
gfp &= GFP_RECLAIM_MASK;
- table = kmalloc_array(memcg->css.cgroup->level, sizeof(*table), gfp);
- if (!table)
- return -ENOMEM;
-
/*
* Because the list_lru can be reparented to the parent cgroup's
* list_lru, we should make sure that this cgroup and all its
* ancestors have allocated list_lru_memcg.
*/
- for (i = 0; memcg; memcg = parent_mem_cgroup(memcg), i++) {
- if (memcg_list_lru_allocated(memcg, lru))
- break;
-
- table[i].memcg = memcg;
- table[i].mlru = memcg_init_list_lru_one(gfp);
- if (!table[i].mlru) {
- while (i--)
- kfree(table[i].mlru);
- kfree(table);
- return -ENOMEM;
+ do {
+ /*
+ * Keep finding the farest parent that wasn't populated
+ * until found memcg itself.
+ */
+ pos = memcg;
+ parent = parent_mem_cgroup(pos);
+ while (parent && !memcg_list_lru_allocated(parent, lru)) {
+ pos = parent;
+ parent = parent_mem_cgroup(pos);
}
- }
- xas_lock_irqsave(&xas, flags);
- while (i--) {
- int index = READ_ONCE(table[i].memcg->kmemcg_id);
- struct list_lru_memcg *mlru = table[i].mlru;
-
- xas_set(&xas, index);
-retry:
- if (unlikely(index < 0 || xas_error(&xas) || xas_load(&xas))) {
- kfree(mlru);
- } else {
- xas_store(&xas, mlru);
- if (xas_error(&xas) == -ENOMEM) {
+ mlru = memcg_init_list_lru_one(gfp);
+ do {
+ bool alloced = false;
+
+ xas_set(&xas, pos->kmemcg_id);
+ xas_lock_irqsave(&xas, flags);
+ if (!css_is_dying(&pos->css) && !xas_load(&xas)) {
+ xas_store(&xas, mlru);
+ alloced = true;
+ }
+ if (!alloced || xas_error(&xas)) {
xas_unlock_irqrestore(&xas, flags);
- if (xas_nomem(&xas, gfp))
- xas_set_err(&xas, 0);
- xas_lock_irqsave(&xas, flags);
- /*
- * The xas lock has been released, this memcg
- * can be reparented before us. So reload
- * memcg id. More details see the comments
- * in memcg_reparent_list_lrus().
- */
- index = READ_ONCE(table[i].memcg->kmemcg_id);
- if (index < 0)
- xas_set_err(&xas, 0);
- else if (!xas_error(&xas) && index != xas.xa_index)
- xas_set(&xas, index);
- goto retry;
+ kfree(mlru);
+ goto out;
}
- }
- }
- /* xas_nomem() is used to free memory instead of memory allocation. */
- if (xas.xa_alloc)
- xas_nomem(&xas, gfp);
- xas_unlock_irqrestore(&xas, flags);
- kfree(table);
-
+ xas_unlock_irqrestore(&xas, flags);
+ } while (xas_nomem(&xas, gfp));
+ } while (pos != memcg);
+out:
return xas_error(&xas);
}
#else
diff --git a/mm/zswap.c b/mm/zswap.c
index a50e2986cd2f..c6e2256347ff 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -718,12 +718,11 @@ static void zswap_lru_add(struct list_lru *list_lru, struct zswap_entry *entry)
/*
* Note that it is safe to use rcu_read_lock() here, even in the face of
- * concurrent memcg offlining. Thanks to the memcg->kmemcg_id indirection
- * used in list_lru lookup, only two scenarios are possible:
+ * concurrent memcg offlining:
*
- * 1. list_lru_add() is called before memcg->kmemcg_id is updated. The
+ * 1. list_lru_add() is called before list_lru_memcg is erased. The
* new entry will be reparented to memcg's parent's list_lru.
- * 2. list_lru_add() is called after memcg->kmemcg_id is updated. The
+ * 2. list_lru_add() is called after list_lru_memcg is erased. The
* new entry will be added directly to memcg's parent's list_lru.
*
* Similar reasoning holds for list_lru_del().
--
2.45.2
