Re: [PATCH 3/3] xfs: allow logical-sector sized O_DIRECT IOs

[Eric Sandeen <sandeen@sandeen.net>]

On 1/20/14, 8:21 AM, Brian Foster wrote:
> On 01/17/2014 03:28 PM, Eric Sandeen wrote:
>> Some time ago, mkfs.xfs started picking the storage physical
>> sector size as the default filesystem "sector size" in order
>> to avoid RMW costs incurred by doing IOs at logical sector
>> size alignments.
>>
>> However, this means that for a filesystem made with i.e.
>> a 4k sector size on an "advanced format" 4k/512 disk,
>> 512-byte direct IOs are no longer allowed.  This means
>> that XFS has essentially turned this AF drive into a hard
>> 4K device, from the filesystem on up.
>>
>> XFS's mkfs-specified "sector size" is really just controlling
>> the minimum size & alignment of filesystem metadata.
>>
>> There is no real need to tightly couple XFS's minimal
>> metadata size to the minimum allowed direct IO size;
>> XFS can continue doing metadata in optimal sizes, but
>> still allow smaller DIOs for apps which issue them,
>> for whatever reason.
>>
>> This patch adds new information to the xfs_buftarg, so that
>> we now track 2 sizes:
>>
>>  1) The metadata sector size, which is the minimum unit and
>>     alignment of IO which will be performed by metadata operations.
>>  2) The device logical sector size.
>>
>> The first is used internally by the file system for metadata
>> alignment and IOs.
>> The second is used for the minimum allowed direct IO size and
>> alignment.
>>
>> This has passed xfstests on filesystems made with 4k sectors,
>> including when run under the patch I sent to ignore
>> XFS_IOC_DIOINFO, and issue 512 DIOs anyway.  I also directly
>> tested end of block behavior on preallocated, sparse, and
>> existing files when we do a 512 IO into a 4k file on a 
>> 4k-sector filesystem, to be sure there were no unexpected
>> behaviors.
>>
>> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
>> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
>> index a526f8d..5175711 100644
>> --- a/fs/xfs/xfs_buf.c
>> +++ b/fs/xfs/xfs_buf.c
>> @@ -1599,6 +1599,7 @@ xfs_setsize_buftarg(
>>  	unsigned int		blocksize,
>>  	unsigned int		sectorsize)
>>  {
>> +	/* Set up metadata sector size info */
>>  	btp->bt_meta_sectorsize = sectorsize;
>>  	btp->bt_meta_sectormask = sectorsize - 1;
>>  
>> @@ -1613,6 +1614,10 @@ xfs_setsize_buftarg(
>>  		return EINVAL;
>>  	}
>>  
>> +	/* Set up device logical sector size mask */
>> +	btp->bt_logical_sectorsize = bdev_logical_block_size(btp->bt_bdev);
>> +	btp->bt_logical_sectormask = bdev_logical_block_size(btp->bt_bdev) - 1;
>> +
>>  	return 0;
>>  }
>>  
>> diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
>> index d5d88dd..9953395 100644
>> --- a/fs/xfs/xfs_buf.h
>> +++ b/fs/xfs/xfs_buf.h
>> @@ -88,6 +88,19 @@ typedef unsigned int xfs_buf_flags_t;
>>   */
>>  #define XFS_BSTATE_DISPOSE	 (1 << 0)	/* buffer being discarded */
>>  
>> +/*
>> + * The xfs_buftarg contains 2 notions of "sector size" -
>> + *
>> + * 1) The metadata sector size, which is the minimum unit and
>> + *    alignment of IO which will be performed by metadata operations.
>> + * 2) The device logical sector size
>> + *
>> + * The first is specified at mkfs time, and is stored on-disk in the
>> + * superblock's sb_sectsize.
>> + *
>> + * The latter is derived from the underlying device, and controls direct IO
>> + * alignment constraints.
>> + */
>>  typedef struct xfs_buftarg {
>>  	dev_t			bt_dev;
>>  	struct block_device	*bt_bdev;
>> @@ -95,6 +108,8 @@ typedef struct xfs_buftarg {
>>  	struct xfs_mount	*bt_mount;
>>  	unsigned int		bt_meta_sectorsize;
>>  	size_t			bt_meta_sectormask;
>> +	size_t			bt_logical_sectorsize;
>> +	size_t			bt_logical_sectormask;
>>  
>>  	/* LRU control structures */
>>  	struct shrinker		bt_shrinker;
>> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
>> index 61a7de0..5507420 100644
>> --- a/fs/xfs/xfs_file.c
>> +++ b/fs/xfs/xfs_file.c
>> @@ -261,7 +261,8 @@ xfs_file_aio_read(
>>  		xfs_buftarg_t	*target =
>>  			XFS_IS_REALTIME_INODE(ip) ?
>>  				mp->m_rtdev_targp : mp->m_ddev_targp;
>> -		if ((pos || size) & target->bt_meta_sectormask) {
>> +		/* DIO must be aligned to device logical sector size */
>> +		if ((pos || size) & target->bt_logical_sectormask) {
>>  			if (pos == i_size_read(inode))
>>  				return 0;
>>  			return -XFS_ERROR(EINVAL);
>> @@ -641,9 +642,11 @@ xfs_file_dio_aio_write(
>>  	struct xfs_buftarg	*target = XFS_IS_REALTIME_INODE(ip) ?
>>  					mp->m_rtdev_targp : mp->m_ddev_targp;
>>  
>> -	if ((pos || count) & target->bt_meta_sectormask)
>> +	/* DIO must be aligned to device logical sector size */
>> +	if ((pos || count) & target->bt_logical_sectormask)
>>  		return -XFS_ERROR(EINVAL);
>>  
> 
> Looks like this requires a v2 to preserve the fixes made in v2 of patch
> 2, unless I missed a newer version of this somewhere.

You're right.  2 diligence demerits for me.  :(

(Hopefully it just wouldn't have applied...)

Maybe I'll just resend the whole series.

Thanks,
-Eric

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