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    Subject[PATCH v8 03/17] mm: Assign id to every memcg-aware shrinker
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    The patch introduces shrinker::id number, which is used to enumerate
    memcg-aware shrinkers. The number start from 0, and the code tries
    to maintain it as small as possible.

    This will be used as to represent a memcg-aware shrinkers in memcg
    shrinkers map.

    Since all memcg-aware shrinkers are based on list_lru, which is per-memcg
    in case of !CONFIG_MEMCG_KMEM only, the new functionality will be under
    this config option.

    Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
    Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
    Tested-by: Shakeel Butt <shakeelb@google.com>
    ---
    include/linux/shrinker.h | 4 +++
    mm/vmscan.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++
    2 files changed, 66 insertions(+)

    diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
    index 6794490f25b2..7ca9c18cf130 100644
    --- a/include/linux/shrinker.h
    +++ b/include/linux/shrinker.h
    @@ -66,6 +66,10 @@ struct shrinker {

    /* These are for internal use */
    struct list_head list;
    +#ifdef CONFIG_MEMCG_KMEM
    + /* ID in shrinker_idr */
    + int id;
    +#endif
    /* objs pending delete, per node */
    atomic_long_t *nr_deferred;
    };
    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index 8d2ffae4db28..f9ca6b57d72f 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -169,6 +169,49 @@ unsigned long vm_total_pages;
    static LIST_HEAD(shrinker_list);
    static DECLARE_RWSEM(shrinker_rwsem);

    +#ifdef CONFIG_MEMCG_KMEM
    +static DEFINE_IDR(shrinker_idr);
    +static int shrinker_nr_max;
    +
    +static int prealloc_memcg_shrinker(struct shrinker *shrinker)
    +{
    + int id, ret = -ENOMEM;
    +
    + down_write(&shrinker_rwsem);
    + id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
    + if (id < 0)
    + goto unlock;
    +
    + if (id >= shrinker_nr_max)
    + shrinker_nr_max = id + 1;
    + shrinker->id = id;
    + ret = 0;
    +unlock:
    + up_write(&shrinker_rwsem);
    + return ret;
    +}
    +
    +static void unregister_memcg_shrinker(struct shrinker *shrinker)
    +{
    + int id = shrinker->id;
    +
    + BUG_ON(id < 0);
    +
    + down_write(&shrinker_rwsem);
    + idr_remove(&shrinker_idr, id);
    + up_write(&shrinker_rwsem);
    +}
    +#else /* CONFIG_MEMCG_KMEM */
    +static int prealloc_memcg_shrinker(struct shrinker *shrinker)
    +{
    + return 0;
    +}
    +
    +static void unregister_memcg_shrinker(struct shrinker *shrinker)
    +{
    +}
    +#endif /* CONFIG_MEMCG_KMEM */
    +
    #ifdef CONFIG_MEMCG
    static bool global_reclaim(struct scan_control *sc)
    {
    @@ -313,13 +356,30 @@ int prealloc_shrinker(struct shrinker *shrinker)
    shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
    if (!shrinker->nr_deferred)
    return -ENOMEM;
    +
    + if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
    + if (prealloc_memcg_shrinker(shrinker))
    + goto free_deferred;
    + }
    +
    return 0;
    +
    +free_deferred:
    + kfree(shrinker->nr_deferred);
    + shrinker->nr_deferred = NULL;
    + return -ENOMEM;
    }

    void free_prealloced_shrinker(struct shrinker *shrinker)
    {
    + if (!shrinker->nr_deferred)
    + return;
    +
    kfree(shrinker->nr_deferred);
    shrinker->nr_deferred = NULL;
    +
    + if (shrinker->flags & SHRINKER_MEMCG_AWARE)
    + unregister_memcg_shrinker(shrinker);
    }

    void register_shrinker_prepared(struct shrinker *shrinker)
    @@ -347,6 +407,8 @@ void unregister_shrinker(struct shrinker *shrinker)
    {
    if (!shrinker->nr_deferred)
    return;
    + if (shrinker->flags & SHRINKER_MEMCG_AWARE)
    + unregister_memcg_shrinker(shrinker);
    down_write(&shrinker_rwsem);
    list_del(&shrinker->list);
    up_write(&shrinker_rwsem);
    \
     
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