Re: [PATCH 2/3] dio: scale unaligned IO tracking via multiple lists

[Jeff Moyer <jmoyer@redhat.com>]

Dave Chinner <david@fromorbit.com> writes:

> From: Dave Chinner <dchinner@redhat.com>
>
> 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@redhat.com>
> ---
>  fs/direct-io.c |   49 ++++++++++++++++++++++++++++++++++++-------------
>  1 files changed, 36 insertions(+), 13 deletions(-)
>
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 1a69efd..353ac52 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -152,8 +152,28 @@ struct dio_zero_block {
>  	atomic_t	ref;		/* reference count */
>  };
>  
> -static DEFINE_SPINLOCK(dio_zero_block_lock);
> -static LIST_HEAD(dio_zero_block_list);
> +#define DIO_ZERO_BLOCK_NR	37LL

I'm always curious to know how these numbers are derived.  Why 37?

Cheers,
Jeff