On Thu, Aug 15, 2024 at 08:54:02AM -0700, Shakeel Butt wrote:
> At the moment memcg IDs are managed through IDR which requires external
> synchronization mechanisms and makes the allocation code a bit awkward.
> Let's switch to xarray and make the code simpler.
>
> Signed-off-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
> Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Reviewed-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
> Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Reviewed-by: Muchun Song <muchun.song@xxxxxxxxx>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
>
> Changes since v1:
> - Fix error path in mem_cgroup_alloc (Dan Carpenter)
>
> mm/memcontrol.c | 39 ++++++++++-----------------------------
> 1 file changed, 10 insertions(+), 29 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index df84683a0e1c..e8e03a5e1e5e 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3408,29 +3408,12 @@ static void memcg_wb_domain_size_changed(struct mem_cgroup *memcg)
> */
>
> #define MEM_CGROUP_ID_MAX ((1UL << MEM_CGROUP_ID_SHIFT) - 1)
> -static DEFINE_IDR(mem_cgroup_idr);
> -static DEFINE_SPINLOCK(memcg_idr_lock);
> -
> -static int mem_cgroup_alloc_id(void)
> -{
> - int ret;
> -
> - idr_preload(GFP_KERNEL);
> - spin_lock(&memcg_idr_lock);
> - ret = idr_alloc(&mem_cgroup_idr, NULL, 1, MEM_CGROUP_ID_MAX + 1,
> - GFP_NOWAIT);
> - spin_unlock(&memcg_idr_lock);
> - idr_preload_end();
> - return ret;
> -}
> +static DEFINE_XARRAY_ALLOC1(mem_cgroup_ids);
>
> static void mem_cgroup_id_remove(struct mem_cgroup *memcg)
> {
> if (memcg->id.id > 0) {
> - spin_lock(&memcg_idr_lock);
> - idr_remove(&mem_cgroup_idr, memcg->id.id);
> - spin_unlock(&memcg_idr_lock);
> -
> + xa_erase(&mem_cgroup_ids, memcg->id.id);
> memcg->id.id = 0;
> }
> }
> @@ -3465,7 +3448,7 @@ static inline void mem_cgroup_id_put(struct mem_cgroup *memcg)
> struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
> {
> WARN_ON_ONCE(!rcu_read_lock_held());
> - return idr_find(&mem_cgroup_idr, id);
> + return xa_load(&mem_cgroup_ids, id);
> }
>
> #ifdef CONFIG_SHRINKER_DEBUG
> @@ -3558,17 +3541,17 @@ static struct mem_cgroup *mem_cgroup_alloc(struct mem_cgroup *parent)
> struct mem_cgroup *memcg;
> int node, cpu;
> int __maybe_unused i;
> - long error = -ENOMEM;
> + long error;
>
> memcg = kzalloc(struct_size(memcg, nodeinfo, nr_node_ids), GFP_KERNEL);
> if (!memcg)
> - return ERR_PTR(error);
> + return ERR_PTR(-ENOMEM);
>
> - memcg->id.id = mem_cgroup_alloc_id();
> - if (memcg->id.id < 0) {
> - error = memcg->id.id;
> + error = xa_alloc(&mem_cgroup_ids, &memcg->id.id, NULL,
> + XA_LIMIT(1, MEM_CGROUP_ID_MAX), GFP_KERNEL);
> + if (error)
> goto fail;
> - }
> + error = -ENOMEM;
There is another subtle change here: xa_alloc() returns -EBUSY in the case
of the address space exhaustion, while the old code returned -ENOSPC.
It's unlikely a big practical problem.
