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

Jan Kara
2016-10-03T09:55:31Z

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@linux.intel.com>
> ---
> 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@suse.com>
SUSE Labs, CR