On Thu, May 27, 2021 at 02:21:44PM +0800, Muchun Song wrote:
> If we run 10k containers in the system, the size of the
> list_lru_memcg->lrus can be ~96KB per list_lru. When we decrease the
> number containers, the size of the array will not be shrinked. It is
> not scalable. The xarray is a good choice for this case. We can save
> a lot of memory when there are tens of thousands continers in the
> system. If we use xarray, we also can remove the logic code of
> resizing array, which can simplify the code.
I am all for this, in concept. Some thoughts below ...
> @@ -56,10 +51,8 @@ struct list_lru {
> #ifdef CONFIG_MEMCG_KMEM
> struct list_head list;
> int shrinker_id;
> - /* protects ->memcg_lrus->lrus[i] */
> - spinlock_t lock;
> /* for cgroup aware lrus points to per cgroup lists, otherwise NULL */
> - struct list_lru_memcg __rcu *memcg_lrus;
> + struct xarray *xa;
> #endif
Normally, we embed an xarray in its containing structure instead of
allocating it. It's only a pointer, int and spinlock, so generally
16 bytes, as opposed to the 8 bytes for the pointer and a 16 byte
allocation. There is a minor wrinkle in that currently 'NULL' is
used to indicate "is not cgroup aware". Maybe there's another way
to indicate that?
> @@ -51,22 +51,12 @@ static int lru_shrinker_id(struct list_lru *lru)
> static inline struct list_lru_one *
> list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
> {
> - struct list_lru_memcg *memcg_lrus;
> - struct list_lru_node *nlru = &lru->node[nid];
> + if (list_lru_memcg_aware(lru) && idx >= 0) {
> + struct list_lru_per_memcg *mlru = xa_load(lru->xa, idx);
>
> - /*
> - * Either lock or RCU protects the array of per cgroup lists
> - * from relocation (see memcg_update_list_lru).
> - */
> - memcg_lrus = rcu_dereference_check(lru->memcg_lrus,
> - lockdep_is_held(&nlru->lock));
> - if (memcg_lrus && idx >= 0) {
> - struct list_lru_per_memcg *mlru;
> -
> - mlru = rcu_dereference_check(memcg_lrus->lrus[idx], true);
> return mlru ? &mlru->nodes[nid] : NULL;
> }
> - return &nlru->lru;
> + return &lru->node[nid].lru;
> }
... perhaps we move the xarray out from under the #ifdef and use index 0
for non-memcg-aware lrus? The XArray is specially optimised for arrays
which only have one entry at 0.
> int list_lru_memcg_alloc(struct list_lru *lru, struct mem_cgroup *memcg, gfp_t gfp)
> {
> + XA_STATE(xas, lru->xa, 0);
> unsigned long flags;
> - struct list_lru_memcg *memcg_lrus;
> - int i;
> + int i, ret = 0;
>
> struct list_lru_memcg_table {
> struct list_lru_per_memcg *mlru;
> @@ -601,22 +522,45 @@ int list_lru_memcg_alloc(struct list_lru *lru, struct mem_cgroup *memcg, gfp_t g
> }
> }
>
> - spin_lock_irqsave(&lru->lock, flags);
> - memcg_lrus = rcu_dereference_protected(lru->memcg_lrus, true);
> + xas_lock_irqsave(&xas, flags);
> while (i--) {
> int index = memcg_cache_id(table[i].memcg);
> struct list_lru_per_memcg *mlru = table[i].mlru;
>
> - if (index < 0 || rcu_dereference_protected(memcg_lrus->lrus[index], true))
> + xas_set(&xas, index);
> +retry:
> + if (unlikely(index < 0 || ret || xas_load(&xas))) {
> kfree(mlru);
> - else
> - rcu_assign_pointer(memcg_lrus->lrus[index], mlru);
> + } else {
> + ret = xa_err(xas_store(&xas, mlru));
This is mixing advanced and normal XArray concepts ... sorry to have
confused you. I think what you meant to do here was:
xas_store(&xas, mlru);
ret = xas_error(&xas);
Or you can avoid introducing 'ret' at all, and keep your errors in the
xa_state. You're kind of mirroring the xa_state errors into 'ret'
anyway, so that seems easier to understand?
> - memcg_id = memcg_alloc_cache_id();
> + memcg_id = ida_simple_get(&memcg_cache_ida, 0, MEMCG_CACHES_MAX_SIZE,
> + GFP_KERNEL);
memcg_id = ida_alloc_max(&memcg_cache_ida,
MEMCG_CACHES_MAX_SIZE - 1, GFP_KERNEL);
... although i think there's actually a fencepost error, and this really
should be MEMCG_CACHES_MAX_SIZE.
> objcg = obj_cgroup_alloc();
> if (!objcg) {
> - memcg_free_cache_id(memcg_id);
> + ida_simple_remove(&memcg_cache_ida, memcg_id);
ida_free(&memcg_cache_ida, memcg_id);
