On Wed, Apr 21, 2021 at 03:00:55PM +0800, Muchun Song wrote:
> In the previous patch, we know how to make the lruvec lock safe when the
> LRU pages reparented. We should do something like following.
>
> memcg_reparent_objcgs(memcg)
> 1) lock
> // lruvec belongs to memcg and lruvec_parent belongs to parent memcg.
> spin_lock(&lruvec->lru_lock);
> spin_lock(&lruvec_parent->lru_lock);
>
> 2) do reparent
> // Move all the pages from the lruvec list to the parent lruvec list.
>
> 3) unlock
> spin_unlock(&lruvec_parent->lru_lock);
> spin_unlock(&lruvec->lru_lock);
>
> Apart from the page lruvec lock, the deferred split queue lock (THP only)
> also needs to do something similar. So we extracted the necessary 3 steps
> in the memcg_reparent_objcgs().
>
> memcg_reparent_objcgs(memcg)
> 1) lock
> memcg_reparent_ops->lock(memcg, parent);
>
> 2) reparent
> memcg_reparent_ops->reparent(memcg, reparent);
>
> 3) unlock
> memcg_reparent_ops->unlock(memcg, reparent);
>
> Now there are two different locks (e.g. lruvec lock and deferred split
> queue lock) need to use this infrastructure. In the next patch, we will
> use those APIs to make those locks safe when the LRU pages reparented.
>
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> ---
> include/linux/memcontrol.h | 11 +++++++++++
> mm/memcontrol.c | 49 ++++++++++++++++++++++++++++++++++++++++++++--
> 2 files changed, 58 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 228263f2c82b..b12847b0be09 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -355,6 +355,17 @@ struct mem_cgroup {
> /* WARNING: nodeinfo must be the last member here */
> };
>
> +struct memcg_reparent_ops {
> + struct list_head list;
> +
> + /* Irq is disabled before calling those functions. */
> + void (*lock)(struct mem_cgroup *memcg, struct mem_cgroup *parent);
> + void (*unlock)(struct mem_cgroup *memcg, struct mem_cgroup *parent);
> + void (*reparent)(struct mem_cgroup *memcg, struct mem_cgroup *parent);
> +};
> +
> +void __init register_memcg_repatent(struct memcg_reparent_ops *ops);
> +
> /*
> * size of first charge trial. "32" comes from vmscan.c's magic value.
> * TODO: maybe necessary to use big numbers in big irons.
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a48403e5999c..f88fe2f06f5b 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -330,6 +330,41 @@ static struct obj_cgroup *obj_cgroup_alloc(void)
> return objcg;
> }
>
> +static LIST_HEAD(reparent_ops_head);
Because this list is completely static, why not make a build-time initialized
array instead?
I guess it's a more canonical way of solving problems like this.
The proposed API looks good to me.
