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    Subject[v8 PATCH 11/13] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers
    Date
    Now nr_deferred is available on per memcg level for memcg aware shrinkers, so don't need
    allocate shrinker->nr_deferred for such shrinkers anymore.

    The prealloc_memcg_shrinker() would return -ENOSYS if !CONFIG_MEMCG or memcg is disabled
    by kernel command line, then shrinker's SHRINKER_MEMCG_AWARE flag would be cleared.
    This makes the implementation of this patch simpler.

    Acked-by: Vlastimil Babka <vbabka@suse.cz>
    Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>
    Acked-by: Roman Gushchin <guro@fb.com>
    Signed-off-by: Yang Shi <shy828301@gmail.com>
    ---
    mm/vmscan.c | 31 ++++++++++++++++---------------
    1 file changed, 16 insertions(+), 15 deletions(-)

    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index 57cbc6bc8a49..d8800e4da67d 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -344,6 +344,9 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
    {
    int id, ret = -ENOMEM;

    + if (mem_cgroup_disabled())
    + return -ENOSYS;
    +
    down_write(&shrinker_rwsem);
    /* This may call shrinker, so it must use down_read_trylock() */
    id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
    @@ -423,7 +426,7 @@ static bool writeback_throttling_sane(struct scan_control *sc)
    #else
    static int prealloc_memcg_shrinker(struct shrinker *shrinker)
    {
    - return 0;
    + return -ENOSYS;
    }

    static void unregister_memcg_shrinker(struct shrinker *shrinker)
    @@ -534,8 +537,18 @@ unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone
    */
    int prealloc_shrinker(struct shrinker *shrinker)
    {
    - unsigned int size = sizeof(*shrinker->nr_deferred);
    + unsigned int size;
    + int err;
    +
    + if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
    + err = prealloc_memcg_shrinker(shrinker);
    + if (err != -ENOSYS)
    + return err;

    + shrinker->flags &= ~SHRINKER_MEMCG_AWARE;
    + }
    +
    + size = sizeof(*shrinker->nr_deferred);
    if (shrinker->flags & SHRINKER_NUMA_AWARE)
    size *= nr_node_ids;

    @@ -543,28 +556,16 @@ int prealloc_shrinker(struct shrinker *shrinker)
    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;
    -
    if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
    down_write(&shrinker_rwsem);
    unregister_memcg_shrinker(shrinker);
    up_write(&shrinker_rwsem);
    + return;
    }

    kfree(shrinker->nr_deferred);
    --
    2.26.2
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