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Subject[PATCH 02/10] mm: Maintain memcg-aware shrinkers in mcg_shrinkers array
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The patch introduces mcg_shrinkers array to keep memcg-aware
shrinkers in order of their shrinker::id.

This allows to access the shrinkers dirrectly by the id,
without iteration over shrinker_list list.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
mm/vmscan.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 81 insertions(+), 8 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 91b5120b924f..97ce4f342fab 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -163,6 +163,46 @@ static DECLARE_RWSEM(shrinker_rwsem);
static DEFINE_IDA(bitmap_id_ida);
static DECLARE_RWSEM(bitmap_rwsem);
static int bitmap_id_start;
+static int bitmap_nr_ids;
+static struct shrinker **mcg_shrinkers;
+
+static int expand_shrinkers_array(int old_nr, int nr)
+{
+ struct shrinker **new;
+ int old_size, size;
+
+ size = nr * sizeof(struct shrinker *);
+ new = kvmalloc(size, GFP_KERNEL);
+ if (!new)
+ return -ENOMEM;
+
+ old_size = old_nr * sizeof(struct shrinker *);
+ memset((void *)new + old_size, 0, size - old_size);
+
+ down_write(&shrinker_rwsem);
+ memcpy((void *)new, mcg_shrinkers, old_size);
+ swap(new, mcg_shrinkers);
+ up_write(&shrinker_rwsem);
+
+ kvfree(new);
+ return 0;
+}
+
+static int expand_shrinker_id(int id)
+{
+ if (likely(id < bitmap_nr_ids))
+ return 0;
+
+ id = bitmap_nr_ids * 2;
+ if (id == 0)
+ id = BITS_PER_BYTE;
+
+ if (expand_shrinkers_array(bitmap_nr_ids, id))
+ return -ENOMEM;
+
+ bitmap_nr_ids = id;
+ return 0;
+}

static int alloc_shrinker_id(struct shrinker *shrinker)
{
@@ -175,8 +215,13 @@ static int alloc_shrinker_id(struct shrinker *shrinker)
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;
+ if (expand_shrinker_id(id)) {
+ ida_remove(&bitmap_id_ida, id);
+ ret = -ENOMEM;
+ } else {
+ shrinker->id = id;
+ bitmap_id_start = shrinker->id + 1;
+ }
}
up_write(&bitmap_rwsem);
if (ret == -EAGAIN)
@@ -198,6 +243,24 @@ static void free_shrinker_id(struct shrinker *shrinker)
bitmap_id_start = id;
up_write(&bitmap_rwsem);
}
+
+static void add_shrinker(struct shrinker *shrinker)
+{
+ down_write(&shrinker_rwsem);
+ if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+ mcg_shrinkers[shrinker->id] = shrinker;
+ list_add_tail(&shrinker->list, &shrinker_list);
+ up_write(&shrinker_rwsem);
+}
+
+static void del_shrinker(struct shrinker *shrinker)
+{
+ down_write(&shrinker_rwsem);
+ if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+ mcg_shrinkers[shrinker->id] = NULL;
+ list_del(&shrinker->list);
+ up_write(&shrinker_rwsem);
+}
#else /* CONFIG_MEMCG && !CONFIG_SLOB */
static int alloc_shrinker_id(struct shrinker *shrinker)
{
@@ -207,6 +270,20 @@ static int alloc_shrinker_id(struct shrinker *shrinker)
static void free_shrinker_id(struct shrinker *shrinker)
{
}
+
+static void add_shrinker(struct shrinker *shrinker)
+{
+ down_write(&shrinker_rwsem);
+ list_add_tail(&shrinker->list, &shrinker_list);
+ up_write(&shrinker_rwsem);
+}
+
+static void del_shrinker(struct shrinker *shrinker)
+{
+ down_write(&shrinker_rwsem);
+ list_del(&shrinker->list);
+ up_write(&shrinker_rwsem);
+}
#endif /* CONFIG_MEMCG && !CONFIG_SLOB */

#ifdef CONFIG_MEMCG
@@ -322,9 +399,7 @@ int register_shrinker(struct shrinker *shrinker)
if (alloc_shrinker_id(shrinker))
goto free_deferred;

- down_write(&shrinker_rwsem);
- list_add_tail(&shrinker->list, &shrinker_list);
- up_write(&shrinker_rwsem);
+ add_shrinker(shrinker);
return 0;

free_deferred:
@@ -341,9 +416,7 @@ void unregister_shrinker(struct shrinker *shrinker)
{
if (!shrinker->nr_deferred)
return;
- down_write(&shrinker_rwsem);
- list_del(&shrinker->list);
- up_write(&shrinker_rwsem);
+ del_shrinker(shrinker);
free_shrinker_id(shrinker);
kfree(shrinker->nr_deferred);
shrinker->nr_deferred = NULL;
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