percpu: rework memcg accounting

The current implementation of the memcg accounting of the percpu
memory is based on the idea of having two separate sets of chunks for
accounted and non-accounted memory. This approach has an advantage
of not wasting any extra memory for memcg data for non-accounted
chunks, however it complicates the code and leads to a higher chunks
number due to a lower chunk utilization.

Instead of having two chunk types it's possible to declare all* chunks
memcg-aware unless the kernel memory accounting is disabled globally
by a boot option. The size of objcg_array is usually small in
comparison to chunks themselves (it obviously depends on the number of
CPUs), so even if some chunk will have no accounted allocations, the
memory waste isn't significant and will likely be compensated by
a higher chunk utilization. Also, with time more and more percpu
allocations will likely become accounted.

* The first chunk is initialized before the memory cgroup subsystem,
  so we don't know for sure whether we need to allocate obj_cgroups.
  Because it's small, let's make it free for use. Then we don't need
  to allocate obj_cgroups for it.

Signed-off-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Dennis Zhou <dennis@kernel.org>

1 files changed, 2 insertions, 3 deletions

diff --git a/mm/percpu-km.c b/mm/percpu-km.c
index c84a9f781a6c..c9d529dc7651 100644
--- a/mm/percpu-km.c
+++ b/mm/percpu-km.c
@@ -44,8 +44,7 @@ static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk,
 	/* nada */
 }
 
-static struct pcpu_chunk *pcpu_create_chunk(enum pcpu_chunk_type type,
-					    gfp_t gfp)
+static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp)
 {
 	const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
 	struct pcpu_chunk *chunk;
@@ -53,7 +52,7 @@ static struct pcpu_chunk *pcpu_create_chunk(enum pcpu_chunk_type type,
 	unsigned long flags;
 	int i;
 
-	chunk = pcpu_alloc_chunk(type, gfp);
+	chunk = pcpu_alloc_chunk(gfp);
 	if (!chunk)
 		return NULL;