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    Subject[v2 PATCH 4/9] mm: vmscan: use a new flag to indicate shrinker is registered
    Date
    Currently registered shrinker is indicated by non-NULL shrinker->nr_deferred.
    This approach is fine with nr_deferred at the shrinker level, but the following
    patches will move MEMCG_AWARE shrinkers' nr_deferred to memcg level, so their
    shrinker->nr_deferred would always be NULL. This would prevent the shrinkers
    from unregistering correctly.

    Introduce a new flag to indicate if shrinker is registered or not.

    Signed-off-by: Yang Shi <shy828301@gmail.com>
    ---
    include/linux/shrinker.h | 7 ++++---
    mm/vmscan.c | 13 +++++++++----
    2 files changed, 13 insertions(+), 7 deletions(-)

    diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
    index 0f80123650e2..1eac79ce57d4 100644
    --- a/include/linux/shrinker.h
    +++ b/include/linux/shrinker.h
    @@ -79,13 +79,14 @@ struct shrinker {
    #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */

    /* Flags */
    -#define SHRINKER_NUMA_AWARE (1 << 0)
    -#define SHRINKER_MEMCG_AWARE (1 << 1)
    +#define SHRINKER_REGISTERED (1 << 0)
    +#define SHRINKER_NUMA_AWARE (1 << 1)
    +#define SHRINKER_MEMCG_AWARE (1 << 2)
    /*
    * It just makes sense when the shrinker is also MEMCG_AWARE for now,
    * non-MEMCG_AWARE shrinker should not have this flag set.
    */
    -#define SHRINKER_NONSLAB (1 << 2)
    +#define SHRINKER_NONSLAB (1 << 3)

    extern int prealloc_shrinker(struct shrinker *shrinker);
    extern void register_shrinker_prepared(struct shrinker *shrinker);
    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index 9b31b9c419ec..16c9d2aeeb26 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -378,6 +378,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
    if (shrinker->flags & SHRINKER_MEMCG_AWARE)
    idr_replace(&shrinker_idr, shrinker, shrinker->id);
    #endif
    + shrinker->flags |= SHRINKER_REGISTERED;
    up_write(&shrinker_rwsem);
    }

    @@ -397,13 +398,17 @@ EXPORT_SYMBOL(register_shrinker);
    */
    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);
    + if (!(shrinker->flags & SHRINKER_REGISTERED)) {
    + up_write(&shrinker_rwsem);
    + return;
    + }
    list_del(&shrinker->list);
    + shrinker->flags &= ~SHRINKER_REGISTERED;
    up_write(&shrinker_rwsem);
    +
    + if (shrinker->flags & SHRINKER_MEMCG_AWARE)
    + unregister_memcg_shrinker(shrinker);
    kfree(shrinker->nr_deferred);
    shrinker->nr_deferred = NULL;
    }
    --
    2.26.2
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