percpu: move fully free chunk reclamation into a work

Impact: code reorganization for later changes

Do fully free chunk reclamation using a work.  This change is to
prepare for locking changes.

Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 38 insertions, 10 deletions

diff --git a/mm/percpu.c b/mm/percpu.c
index 7d9bc35e8ed2..4c8a419119da 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -63,6 +63,7 @@
 #include <linux/rbtree.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
+#include <linux/workqueue.h>
 
 #include <asm/cacheflush.h>
 #include <asm/tlbflush.h>
@@ -118,6 +119,10 @@ static DEFINE_MUTEX(pcpu_mutex);
 static struct list_head *pcpu_slot __read_mostly; /* chunk list slots */
 static struct rb_root pcpu_addr_root = RB_ROOT; /* chunks by address */
 
+/* reclaim work to release fully free chunks, scheduled from free path */
+static void pcpu_reclaim(struct work_struct *work);
+static DECLARE_WORK(pcpu_reclaim_work, pcpu_reclaim);
+
 static int __pcpu_size_to_slot(int size)
 {
         int highbit = fls(size);        /* size is in bytes */
@@ -846,13 +851,37 @@ void *__alloc_reserved_percpu(size_t size, size_t align)
         return pcpu_alloc(size, align, true);
 }
 
-static void pcpu_kill_chunk(struct pcpu_chunk *chunk)
+/**
+ * pcpu_reclaim - reclaim fully free chunks, workqueue function
+ * @work: unused
+ *
+ * Reclaim all fully free chunks except for the first one.
+ */
+static void pcpu_reclaim(struct work_struct *work)
 {
-        WARN_ON(chunk->immutable);
-        pcpu_depopulate_chunk(chunk, 0, pcpu_unit_size, false);
-        list_del(&chunk->list);
-        rb_erase(&chunk->rb_node, &pcpu_addr_root);
-        free_pcpu_chunk(chunk);
+        LIST_HEAD(todo);
+        struct list_head *head = &pcpu_slot[pcpu_nr_slots - 1];
+        struct pcpu_chunk *chunk, *next;
+
+        mutex_lock(&pcpu_mutex);
+
+        list_for_each_entry_safe(chunk, next, head, list) {
+                WARN_ON(chunk->immutable);
+
+                /* spare the first one */
+                if (chunk == list_first_entry(head, struct pcpu_chunk, list))
+                        continue;
+
+                rb_erase(&chunk->rb_node, &pcpu_addr_root);
+                list_move(&chunk->list, &todo);
+        }
+
+        mutex_unlock(&pcpu_mutex);
+
+        list_for_each_entry_safe(chunk, next, &todo, list) {
+                pcpu_depopulate_chunk(chunk, 0, pcpu_unit_size, false);
+                free_pcpu_chunk(chunk);
+        }
 }
 
 /**
@@ -877,14 +906,13 @@ void free_percpu(void *ptr)
 
         pcpu_free_area(chunk, off);
 
-        /* the chunk became fully free, kill one if there are other free ones */
+        /* if there are more than one fully free chunks, wake up grim reaper */
         if (chunk->free_size == pcpu_unit_size) {
                 struct pcpu_chunk *pos;
 
-                list_for_each_entry(pos,
-                                    &pcpu_slot[pcpu_chunk_slot(chunk)], list)
+                list_for_each_entry(pos, &pcpu_slot[pcpu_nr_slots - 1], list)
                         if (pos != chunk) {
-                                pcpu_kill_chunk(pos);
+                                schedule_work(&pcpu_reclaim_work);
                                 break;
                         }
         }