On 4/2/19 4:31 PM, Dave Chinner wrote:
> On Tue, Apr 02, 2019 at 10:56:32AM -0700, Darrick J. Wong wrote:
>> On Tue, Apr 02, 2019 at 10:44:38AM -0500, Eric Sandeen wrote:
>>> pmem is byte addressable, and indeed byte-aligned DIO works on
>>> a DAX file. So, teach XFS_IOC_DIOINFO to return the correct
>>> alignment information if IS_DAX(inode).
>>
>> If it's a DAX filesystem, do we want to try to steer people towards
>> things like 2MB pages since (in theory) we can get away with fewer page
>> table mappings? And (seeing as that's mmap that cares, not directio)
>> would advertising preferential page mapping sizes be more appropriate
>> advertised in a different ioctl?
>>
>> --D
>>
>>> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
>>> ---
>>>
>>> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
>>> index 6ecdbb3..35eae7d 100644
>>> --- a/fs/xfs/xfs_ioctl.c
>>> +++ b/fs/xfs/xfs_ioctl.c
>>> @@ -1919,12 +1919,21 @@ xfs_file_ioctl(
>>> }
>>> case XFS_IOC_DIOINFO: {
>>> struct dioattr da;
>>> - xfs_buftarg_t *target =
>>> - XFS_IS_REALTIME_INODE(ip) ?
>>> - mp->m_rtdev_targp : mp->m_ddev_targp;
>>>
>>> - da.d_mem = da.d_miniosz = target->bt_logical_sectorsize;
>>> - da.d_maxiosz = INT_MAX & ~(da.d_miniosz - 1);
>>> + if (IS_DAX(inode)) {
>>> + /* pmem is byte addressable */
>>> + da.d_mem = 1;
>>> + da.d_miniosz = 1;
>>> + da.d_maxiosz = INT_MAX;
>
> I don't think we want to open that can of worms.
It's already open... byte-granularity dax+dio succeeds today.
Does it work? ;)
> Have you run fsx on dax mixing mmap/dio with byte range granularity?
Like:
# fsx -Z -r 1 -w 1 daxfile
?
yes (now that you asked) ;)
not to a bazillion ops, but I've not seen a failure yet.
This is on simulated pmem, on a 5.0 kernel.
-Eric
> Cheers,
>
> Dave.
>
