percpu: expose statistics about percpu memory via debugfs

There is limited visibility into the use of percpu memory leaving us
unable to reason about correctness of parameters and overall use of
percpu memory. These counters and statistics aim to help understand
basic statistics about percpu memory such as number of allocations over
the lifetime, allocation sizes, and fragmentation.

New Config: PERCPU_STATS

Signed-off-by: Dennis Zhou <dennisz@fb.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/mm/percpu.c b/mm/percpu.c
index 75ac982c19df..44a1cadf74a7 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -657,6 +657,7 @@ static void pcpu_free_area(struct pcpu_chunk *chunk, int freeme,
         int *p;
 
         lockdep_assert_held(&pcpu_lock);
+        pcpu_stats_area_dealloc(chunk);
 
         freeme |= 1;    /* we are searching for <given offset, in use> pair */
 
@@ -721,6 +722,7 @@ static struct pcpu_chunk *pcpu_alloc_chunk(void)
         chunk->map[0] = 0;
         chunk->map[1] = pcpu_unit_size | 1;
         chunk->map_used = 1;
+        chunk->has_reserved = false;
 
         INIT_LIST_HEAD(&chunk->list);
         INIT_LIST_HEAD(&chunk->map_extend_list);
@@ -970,6 +972,7 @@ restart:
         goto restart;
 
 area_found:
+        pcpu_stats_area_alloc(chunk, size);
         spin_unlock_irqrestore(&pcpu_lock, flags);
 
         /* populate if not all pages are already there */
@@ -1642,6 +1645,8 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
         pcpu_chunk_struct_size = sizeof(struct pcpu_chunk) +
                 BITS_TO_LONGS(pcpu_unit_pages) * sizeof(unsigned long);
 
+        pcpu_stats_save_ai(ai);
+
         /*
          * Allocate chunk slots.  The additional last slot is for
          * empty chunks.
@@ -1685,6 +1690,7 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
         if (schunk->free_size)
                 schunk->map[++schunk->map_used] = ai->static_size + schunk->free_size;
         schunk->map[schunk->map_used] |= 1;
+        schunk->has_reserved = true;
 
         /* init dynamic chunk if necessary */
         if (dyn_size) {
@@ -1703,6 +1709,7 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
                 dchunk->map[1] = pcpu_reserved_chunk_limit;
                 dchunk->map[2] = (pcpu_reserved_chunk_limit + dchunk->free_size) | 1;
                 dchunk->map_used = 2;
+                dchunk->has_reserved = true;
         }
 
         /* link the first chunk in */
@@ -1711,6 +1718,8 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
                 pcpu_count_occupied_pages(pcpu_first_chunk, 1);
         pcpu_chunk_relocate(pcpu_first_chunk, -1);
 
+        pcpu_stats_chunk_alloc();
+
         /* we're done */
         pcpu_base_addr = base_addr;
         return 0;