new_inode() dirties a contended cache line to get increasing
inode numbers.
Solve this problem by providing to each cpu a per_cpu variable,
feeded by the shared last_ino, but once every 1024 allocations.
This reduce contention on the shared last_ino, and give same
spreading ino numbers than before.
(same wraparound after 2^32 allocations)
Signed-off-by: Eric Dumazet <dada1@xxxxxxxxxxxxx>
---
fs/inode.c | 35 ++++++++++++++++++++++++++++++++---
1 files changed, 32 insertions(+), 3 deletions(-)
diff --git a/fs/inode.c b/fs/inode.c
index f94f889..dc8e72a 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -556,6 +556,36 @@ repeat:
return node ? inode : NULL;
}
+#ifdef CONFIG_SMP
+/*
+ * Each cpu owns a range of 1024 numbers.
+ * 'shared_last_ino' is dirtied only once out of 1024 allocations,
+ * to renew the exhausted range.
+ */
+static DEFINE_PER_CPU(int, last_ino);
+
+static int last_ino_get(void)
+{
+ static atomic_t shared_last_ino;
+ int *p = &get_cpu_var(last_ino);
+ int res = *p;
+
+ if (unlikely((res & 1023) == 0))
+ res = atomic_add_return(1024, &shared_last_ino) - 1024;
+
+ *p = ++res;
+ put_cpu_var(last_ino);
+ return res;
+}
+#else
+static int last_ino_get(void)
+{
+ static int last_ino;
+
+ return ++last_ino;
+}
+#endif
+
/**
* new_inode - obtain an inode
* @sb: superblock
@@ -575,7 +605,6 @@ struct inode *new_inode(struct super_block *sb)
* error if st_ino won't fit in target struct field. Use 32bit counter
* here to attempt to avoid that.
*/
- static unsigned int last_ino;
struct inode * inode;
spin_lock_prefetch(&inode_lock);
@@ -583,11 +612,11 @@ struct inode *new_inode(struct super_block *sb)
inode = alloc_inode(sb);
if (inode) {
percpu_counter_inc(&nr_inodes);
+ inode->i_state = 0;
+ inode->i_ino = last_ino_get();
spin_lock(&inode_lock);
list_add(&inode->i_list, &inode_in_use);
list_add(&inode->i_sb_list, &sb->s_inodes);
- inode->i_ino = ++last_ino;
- inode->i_state = 0;
spin_unlock(&inode_lock);
}
return inode;
