Re: [PATCH v3 07/11] mm: vmalloc: Offload free_vmap_area_lock lock

Hillf Danton
2024-01-03T11:08:53Z

On Tue, 2 Jan 2024 19:46:29 +0100 Uladzislau Rezki <urezki@gmail.com>
> +static void
> +decay_va_pool_node(struct vmap_node *vn, bool full_decay)
> +{
> + struct vmap_area *va, *nva;
> + struct list_head decay_list;
> + struct rb_root decay_root;
> + unsigned long n_decay;
> + int i;
> +
> + decay_root = RB_ROOT;
> + INIT_LIST_HEAD(&decay_list);
> +
> + for (i = 0; i < MAX_VA_SIZE_PAGES; i++) {
> + struct list_head tmp_list;
> +
> + if (list_empty(&vn->pool[i].head))
> + continue;
> +
> + INIT_LIST_HEAD(&tmp_list);
> +
> + /* Detach the pool, so no-one can access it. */
> + spin_lock(&vn->pool_lock);
> + list_replace_init(&vn->pool[i].head, &tmp_list);
> + spin_unlock(&vn->pool_lock);
> +
> + if (full_decay)
> + WRITE_ONCE(vn->pool[i].len, 0);
> +
> + /* Decay a pool by ~25% out of left objects. */
> + n_decay = vn->pool[i].len >> 2;
> +
> + list_for_each_entry_safe(va, nva, &tmp_list, list) {
> + list_del_init(&va->list);
> + merge_or_add_vmap_area(va, &decay_root, &decay_list);
> +
> + if (!full_decay) {
> + WRITE_ONCE(vn->pool[i].len, vn->pool[i].len - 1);
> +
> + if (!--n_decay)
> + break;
> + }
> + }
> +
> + /* Attach the pool back if it has been partly decayed. */
> + if (!full_decay && !list_empty(&tmp_list)) {
> + spin_lock(&vn->pool_lock);
> + list_replace_init(&tmp_list, &vn->pool[i].head);
> + spin_unlock(&vn->pool_lock);
> + }

Failure of working out why list_splice() was not used here in case of
non-empty vn->pool[i].head, after staring ten minutes.
> + }
> +
> + reclaim_list_global(&decay_list);
> +}