diff options
authorRoman Gushchin <>2020-08-11 18:30:14 -0700
committerLinus Torvalds <>2020-08-12 10:57:55 -0700
commit5b32af91b5de6f95ad99e4eaaf57777376af124f (patch)
parent00e4db51259a5f936fec1424b884f029479d3981 (diff)
percpu: return number of released bytes from pcpu_free_area()
Patch series "mm: memcg accounting of percpu memory", v3. This patchset adds percpu memory accounting to memory cgroups. It's based on the rework of the slab controller and reuses concepts and features introduced for the per-object slab accounting. Percpu memory is becoming more and more widely used by various subsystems, and the total amount of memory controlled by the percpu allocator can make a good part of the total memory. As an example, bpf maps can consume a lot of percpu memory, and they are created by a user. Also, some cgroup internals (e.g. memory controller statistics) can be quite large. On a machine with many CPUs and big number of cgroups they can consume hundreds of megabytes. So the lack of memcg accounting is creating a breach in the memory isolation. Similar to the slab memory, percpu memory should be accounted by default. Percpu allocations by their nature are scattered over multiple pages, so they can't be tracked on the per-page basis. So the per-object tracking introduced by the new slab controller is reused. The patchset implements charging of percpu allocations, adds memcg-level statistics, enables accounting for percpu allocations made by memory cgroup internals and provides some basic tests. To implement the accounting of percpu memory without a significant memory and performance overhead the following approach is used: all accounted allocations are placed into a separate percpu chunk (or chunks). These chunks are similar to default chunks, except that they do have an attached vector of pointers to obj_cgroup objects, which is big enough to save a pointer for each allocated object. On the allocation, if the allocation has to be accounted (__GFP_ACCOUNT is passed, the allocating process belongs to a non-root memory cgroup, etc), the memory cgroup is getting charged and if the maximum limit is not exceeded the allocation is performed using a memcg-aware chunk. Otherwise -ENOMEM is returned or the allocation is forced over the limit, depending on gfp (as any other kernel memory allocation). The memory cgroup information is saved in the obj_cgroup vector at the corresponding offset. On the release time the memcg information is restored from the vector and the cgroup is getting uncharged. Unaccounted allocations (at this point the absolute majority of all percpu allocations) are performed in the old way, so no additional overhead is expected. To avoid pinning dying memory cgroups by outstanding allocations, obj_cgroup API is used instead of directly saving memory cgroup pointers. obj_cgroup is basically a pointer to a memory cgroup with a standalone reference counter. The trick is that it can be atomically swapped to point at the parent cgroup, so that the original memory cgroup can be released prior to all objects, which has been charged to it. Because all charges and statistics are fully recursive, it's perfectly correct to uncharge the parent cgroup instead. This scheme is used in the slab memory accounting, and percpu memory can just follow the scheme. This patch (of 5): To implement accounting of percpu memory we need the information about the size of freed object. Return it from pcpu_free_area(). Signed-off-by: Roman Gushchin <> Signed-off-by: Andrew Morton <> Reviewed-by: Shakeel Butt <> Acked-by: Dennis Zhou <> Cc: Tejun Heo <> Cc: Christoph Lameter <> Cc: Johannes Weiner <> Cc: Michal Hocko <> Cc: David Rientjes <> Cc: Joonsoo Kim <> Cc: Mel Gorman <> Cc: Pekka Enberg <> Cc: Tobin C. Harding <> Cc: Vlastimil Babka <> Cc: Waiman Long <> cC: Michal Koutný> Cc: Bixuan Cui <> Cc: Michal Koutný <> Cc: Stephen Rothwell <> Link: Link: Link: Signed-off-by: Linus Torvalds <>
1 files changed, 10 insertions, 3 deletions
diff --git a/mm/percpu.c b/mm/percpu.c
index b626766160ce..5e9eefdce21f 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1211,11 +1211,14 @@ static int pcpu_alloc_area(struct pcpu_chunk *chunk, int alloc_bits,
* This function determines the size of an allocation to free using
* the boundary bitmap and clears the allocation map.
+ *
+ * Number of freed bytes.
-static void pcpu_free_area(struct pcpu_chunk *chunk, int off)
+static int pcpu_free_area(struct pcpu_chunk *chunk, int off)
struct pcpu_block_md *chunk_md = &chunk->chunk_md;
- int bit_off, bits, end, oslot;
+ int bit_off, bits, end, oslot, freed;
@@ -1230,8 +1233,10 @@ static void pcpu_free_area(struct pcpu_chunk *chunk, int off)
bits = end - bit_off;
bitmap_clear(chunk->alloc_map, bit_off, bits);
+ freed = bits * PCPU_MIN_ALLOC_SIZE;
/* update metadata */
- chunk->free_bytes += bits * PCPU_MIN_ALLOC_SIZE;
+ chunk->free_bytes += freed;
/* update first free bit */
chunk_md->first_free = min(chunk_md->first_free, bit_off);
@@ -1239,6 +1244,8 @@ static void pcpu_free_area(struct pcpu_chunk *chunk, int off)
pcpu_block_update_hint_free(chunk, bit_off, bits);
pcpu_chunk_relocate(chunk, oslot);
+ return freed;
static void pcpu_init_md_block(struct pcpu_block_md *block, int nr_bits)