On 4/2/19 12:56 PM, 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?
The xfsctl(3) manpage documents XFS_IOC_DIOINFO as providing the
minimum/required alignments to avoid DIO failure. Says nothing about
optimal. So, if you'd like to advertise preferences, it seems like
this is not the interface to use...
-Eric
> --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;
>> + } else {
>> + xfs_buftarg_t *target =
>> + XFS_IS_REALTIME_INODE(ip) ?
>> + mp->m_rtdev_targp : mp->m_ddev_targp;
>> +
>> + da.d_mem = target->bt_logical_sectorsize;
>> + da.d_miniosz = target->bt_logical_sectorsize;
>> + da.d_maxiosz = INT_MAX & ~(da.d_miniosz - 1);
>> + }
>>
>> if (copy_to_user(arg, &da, sizeof(da)))
>> return -EFAULT;
>>
