On Thu, Dec 11, 2008 at 11:39:18PM +0100, Eric Dumazet wrote:
> 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)
One question below, but just a clarification. Works correctly as is,
though a bit strangely.
Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> 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;
So the first CPU gets the range [1:1024], the second [1025:2048], and
so on, eventually wrapping to [4294966273:0]. Is that the intent?
(I don't see a problem with this, just seems a bit strange.)
> + 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;
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
