Re: [PATCH 3/8] xarray: Explicitely set XA_FREE_MARK in __xa_cmpxchg()

[Jason Gunthorpe <jgg@xxxxxxxx>]

On Tue, Feb 04, 2020 at 03:25:09PM +0100, Jan Kara wrote:
> __xa_cmpxchg() relies on xas_store() to set XA_FREE_MARK when storing
> NULL into xarray that has free tracking enabled. Make the setting of
> XA_FREE_MARK explicit similarly as its clearing currently it.
> 
> Signed-off-by: Jan Kara <jack@xxxxxxx>
>  lib/xarray.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/xarray.c b/lib/xarray.c
> index ae8b7070e82c..4e32497c51bd 100644
> +++ b/lib/xarray.c
> @@ -1477,8 +1477,12 @@ void *__xa_cmpxchg(struct xarray *xa, unsigned long index,
>  		curr = xas_load(&xas);
>  		if (curr == old) {
>  			xas_store(&xas, entry);
> -			if (xa_track_free(xa) && entry && !curr)
> -				xas_clear_mark(&xas, XA_FREE_MARK);
> +			if (xa_track_free(xa)) {
> +				if (entry && !curr)
> +					xas_clear_mark(&xas, XA_FREE_MARK);
> +				else if (!entry && curr)
> +					xas_set_mark(&xas, XA_FREE_MARK);
> +			}

This feels like an optimization that should also happen for
__xa_store, which has very similar code:

		curr = xas_store(&xas, entry);
		if (xa_track_free(xa))
			xas_clear_mark(&xas, XA_FREE_MARK);

Something like

                if (xa_track_free(xa) && entry && !curr)
			xas_clear_mark(&xas, XA_FREE_MARK);

?

Regards,
Jason