new_inode() dirties a contended cache line to get 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.
Note : last_ino_get() method must be called with preemption
disabled on SMP.
(socket8 bench result : no differences, but this is because inode_lock
cost is too heavy)
Signed-off-by: Eric Dumazet <dada1@xxxxxxxxxxxxx>
---
fs/inode.c | 27 +++++++++++++++++++++++++--
1 files changed, 25 insertions(+), 2 deletions(-)
diff --git a/fs/inode.c b/fs/inode.c
index 0487ddb..d850050 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -534,6 +534,30 @@ repeat:
return node ? inode : NULL;
}
+#ifdef CONFIG_SMP
+/*
+ * each cpu owns a block of 1024 numbers.
+ * The global 'last_ino' is dirtied once every 1024 allocations
+ */
+static DEFINE_PER_CPU(int, cpu_ino_alloc) = {0};
+static int last_ino_get(void)
+{
+ static atomic_t last_ino;
+ int *ptr = &__raw_get_cpu_var(cpu_ino_alloc);
+
+ if (unlikely((*ptr & 1023) == 0))
+ *ptr = atomic_add_return(1024, &last_ino);
+ return --(*ptr);
+}
+#else
+static int last_ino_get(void)
+{
+ static int last_ino;
+
+ return ++last_ino;
+}
+#endif
+
/**
* new_inode - obtain an inode
* @sb: superblock
@@ -553,7 +577,6 @@ 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);
@@ -564,7 +587,7 @@ struct inode *new_inode(struct super_block *sb)
inodes_stat.nr_inodes++;
list_add(&inode->i_list, &inode_in_use);
list_add(&inode->i_sb_list, &sb->s_inodes);
- inode->i_ino = ++last_ino;
+ inode->i_ino = last_ino_get();
inode->i_state = 0;
spin_unlock(&inode_lock);
}
