Re: [PATCH v4 07/12] dax: coordinate locking for offsets in PMD range

[Jan Kara]

On Thu 29-09-16 16:49:25, Ross Zwisler wrote:
> DAX radix tree locking currently locks entries based on the unique
> combination of the 'mapping' pointer and the pgoff_t 'index' for the entry.
> This works for PTEs, but as we move to PMDs we will need to have all the
> offsets within the range covered by the PMD to map to the same bit lock.
> To accomplish this, for ranges covered by a PMD entry we will instead lock
> based on the page offset of the beginning of the PMD entry.  The 'mapping'
> pointer is still used in the same way.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> ---
>  fs/dax.c            | 37 ++++++++++++++++++++++++-------------
>  include/linux/dax.h |  2 +-
>  mm/filemap.c        |  2 +-
>  3 files changed, 26 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index baef586..406feea 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -64,10 +64,17 @@ static int __init init_dax_wait_table(void)
>  }
>  fs_initcall(init_dax_wait_table);
>  
> +static pgoff_t dax_entry_start(pgoff_t index, void *entry)
> +{
> +	if (RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
> +		index &= (PMD_MASK >> PAGE_SHIFT);

Hum, but if we shift right, top bits of PMD_MASK will become zero - not
something we want I guess... You rather want to mask with something like:
	~((1UL << (PMD_SHIFT - PAGE_SHIFT)) - 1)

> @@ -447,10 +457,11 @@ restart:
>  	return entry;
>  }
>  
> -void dax_wake_mapping_entry_waiter(struct address_space *mapping,
> +void dax_wake_mapping_entry_waiter(void *entry, struct address_space *mapping,
>  				   pgoff_t index, bool wake_all)

Nitpick: Ordering of arguments would look more logical to me like:

dax_wake_mapping_entry_waiter(mapping, index, entry, wake_all)

Other than that the patch looks good to me.

								Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR