On Fri 09-08-24 10:26:18, 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.
>
> Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Signed-off-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Neat! I was not aware of this feature of XArray. Is there any actual
reason for idr to have its own implementation with XArray offering a
better interface?
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Thanks!
> ---
> mm/memcontrol.c | 34 +++++++---------------------------
> 1 file changed, 7 insertions(+), 27 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e1ffd2950393..b8e6b98485c6 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3363,29 +3363,12 @@ 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;
> }
> }
> @@ -3420,7 +3403,7 @@ 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
> @@ -3519,11 +3502,10 @@ static struct mem_cgroup *mem_cgroup_alloc(struct mem_cgroup *parent)
> if (!memcg)
> return ERR_PTR(error);
>
> - 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;
> - }
>
> memcg->vmstats = kzalloc(sizeof(struct memcg_vmstats),
> GFP_KERNEL_ACCOUNT);
> @@ -3664,9 +3646,7 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css)
> * publish it here at the end of onlining. This matches the
> * regular ID destruction during offlining.
> */
> - spin_lock(&memcg_idr_lock);
> - idr_replace(&mem_cgroup_idr, memcg, memcg->id.id);
> - spin_unlock(&memcg_idr_lock);
> + xa_store(&mem_cgroup_ids, memcg->id.id, memcg, GFP_KERNEL);
>
> return 0;
> offline_kmem:
> --
> 2.43.5
>
--
Michal Hocko
SUSE Labs
