[patch 42/52] fs: icache per-cpu last_ino allocator

npiggin
2010-06-24T03:26:19Z

[-- Attachment #1: fs-last_ino-percpu.patch --]
[-- Type: text/plain, Size: 2362 bytes --]

From: Eric Dumazet <dada1@cosmosbay.com>

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@cosmosbay.com>
Signed-off-by: Nick Piggin <npiggin@suse.de>
---
fs/inode.c | 42 +++++++++++++++++++++++++++++++++++-------
1 file changed, 35 insertions(+), 7 deletions(-)

Index: linux-2.6/fs/inode.c
===================================================================
--- linux-2.6.orig/fs/inode.c
+++ linux-2.6/fs/inode.c
@@ -664,6 +664,40 @@ __inode_add_to_lists(struct super_block
}
}

+#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.
+ *
+ * On a 32bit, non LFS stat() call, glibc will generate an EOVERFLOW
+ * error if st_ino won't fit in target struct field. Use 32bit counter
+ * here to attempt to avoid that.
+ */
+static DEFINE_PER_CPU(int, last_ino);
+static atomic_t shared_last_ino;
+
+static int last_ino_get(void)
+{
+ 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
+
/**
* inode_add_to_lists - add a new inode to relevant lists
* @sb: superblock inode belongs to
@@ -700,19 +734,13 @@ EXPORT_SYMBOL_GPL(inode_add_to_lists);
*/
struct inode *new_inode(struct super_block *sb)
{
- /*
- * On a 32bit, non LFS stat() call, glibc will generate an EOVERFLOW
- * error if st_ino won't fit in target struct field. Use 32bit counter
- * here to attempt to avoid that.
- */
- static atomic_t last_ino = ATOMIC_INIT(0);
struct inode *inode;

inode = alloc_inode(sb);
if (inode) {
/* XXX: init as locked for speedup */
spin_lock(&inode->i_lock);
- inode->i_ino = atomic_inc_return(&last_ino);
+ inode->i_ino = last_ino_get();
inode->i_state = 0;
__inode_add_to_lists(sb, NULL, inode);
spin_unlock(&inode->i_lock);