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    Subject[PATCH 01/10] 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.

    Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
    ---
    include/linux/shrinker.h | 1 +
    mm/vmscan.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++
    2 files changed, 60 insertions(+)

    diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
    index a3894918a436..738de8ef5246 100644
    --- a/include/linux/shrinker.h
    +++ b/include/linux/shrinker.h
    @@ -66,6 +66,7 @@ struct shrinker {

    /* These are for internal use */
    struct list_head list;
    + int id;
    /* objs pending delete, per node */
    atomic_long_t *nr_deferred;
    };
    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index 8fcd9f8d7390..91b5120b924f 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -159,6 +159,56 @@ unsigned long vm_total_pages;
    static LIST_HEAD(shrinker_list);
    static DECLARE_RWSEM(shrinker_rwsem);

    +#if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB)
    +static DEFINE_IDA(bitmap_id_ida);
    +static DECLARE_RWSEM(bitmap_rwsem);
    +static int bitmap_id_start;
    +
    +static int alloc_shrinker_id(struct shrinker *shrinker)
    +{
    + int id, ret;
    +
    + if (!(shrinker->flags & SHRINKER_MEMCG_AWARE))
    + return 0;
    +retry:
    + ida_pre_get(&bitmap_id_ida, GFP_KERNEL);
    + down_write(&bitmap_rwsem);
    + ret = ida_get_new_above(&bitmap_id_ida, bitmap_id_start, &id);
    + if (!ret) {
    + shrinker->id = id;
    + bitmap_id_start = shrinker->id + 1;
    + }
    + up_write(&bitmap_rwsem);
    + if (ret == -EAGAIN)
    + goto retry;
    +
    + return ret;
    +}
    +
    +static void free_shrinker_id(struct shrinker *shrinker)
    +{
    + int id = shrinker->id;
    +
    + if (!(shrinker->flags & SHRINKER_MEMCG_AWARE))
    + return;
    +
    + down_write(&bitmap_rwsem);
    + ida_remove(&bitmap_id_ida, id);
    + if (bitmap_id_start > id)
    + bitmap_id_start = id;
    + up_write(&bitmap_rwsem);
    +}
    +#else /* CONFIG_MEMCG && !CONFIG_SLOB */
    +static int alloc_shrinker_id(struct shrinker *shrinker)
    +{
    + return 0;
    +}
    +
    +static void free_shrinker_id(struct shrinker *shrinker)
    +{
    +}
    +#endif /* CONFIG_MEMCG && !CONFIG_SLOB */
    +
    #ifdef CONFIG_MEMCG
    static bool global_reclaim(struct scan_control *sc)
    {
    @@ -269,10 +319,18 @@ int register_shrinker(struct shrinker *shrinker)
    if (!shrinker->nr_deferred)
    return -ENOMEM;

    + if (alloc_shrinker_id(shrinker))
    + goto free_deferred;
    +
    down_write(&shrinker_rwsem);
    list_add_tail(&shrinker->list, &shrinker_list);
    up_write(&shrinker_rwsem);
    return 0;
    +
    +free_deferred:
    + kfree(shrinker->nr_deferred);
    + shrinker->nr_deferred = NULL;
    + return -ENOMEM;
    }
    EXPORT_SYMBOL(register_shrinker);

    @@ -286,6 +344,7 @@ void unregister_shrinker(struct shrinker *shrinker)
    down_write(&shrinker_rwsem);
    list_del(&shrinker->list);
    up_write(&shrinker_rwsem);
    + free_shrinker_id(shrinker);
    kfree(shrinker->nr_deferred);
    shrinker->nr_deferred = NULL;
    }
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