On Mon, Aug 02, 2010 at 05:25:45PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> To avoid concerns that a single list and lock tracking the unaligned IOs
> will not scale appropriately, create multiple lists and locks and chose them by
> hashing the unaligned block being zeroed.
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
> fs/direct-io.c | 53 ++++++++++++++++++++++++++++++++++++++++-------------
> 1 files changed, 40 insertions(+), 13 deletions(-)
>
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 611524e..95dcba4 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -152,8 +152,29 @@ struct dio_zero_block {
> atomic_t ref; /* reference count */
> };
>
> -DEFINE_SPINLOCK(dio_zero_block_lock);
> -LIST_HEAD(dio_zero_block_list);
> +#define DIO_ZERO_BLOCK_NR 37LL
> +struct dio_zero_block_head {
> + struct list_head list;
> + spinlock_t lock;
> +};
> +
> +struct dio_zero_block_head dio_zero_blocks[DIO_ZERO_BLOCK_NR];
Again, should be static.
> +#define to_dio_zero_list(zb) (&dio_zero_blocks[zb % DIO_ZERO_BLOCK_NR].list)
> +#define to_dio_zero_lock(zb) (&dio_zero_blocks[zb % DIO_ZERO_BLOCK_NR].lock)
> + struct list_head *list = to_dio_zero_list(zero_block);
> + spinlock_t *lock = to_dio_zero_lock(zero_block);
What about just finding the dio_zero_block_head and stuffing it into
a local variable? Probably doesn't matter in the end anyway.
Also looks good.
If people really care about making this scale better we could also make
it per-sb.
One really big problem is that no one tells the users that unaligned
direct I/O is a performance problem. We should add a variant of the
XFS DIOINFO ioctl to the core VFS, including minimally required and
optimal alignment values.
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