Re: [PATCH v5 4/4]xfs: xfs_seek_hole() refinements with lookup hole offset from page cache.

[Jie Liu <jeff.liu@oracle.com>]

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On 07/31/12 08:13, Dave Chinner wrote:
> On Thu, Jul 26, 2012 at 04:56:22PM +0800, Jeff Liu wrote:
>> Search possbile hole offset for given range from page cache for unwritten and delayed-allocation extents.
>>
>> Signed-off-by: Jie Liu <jeff.liu@oracle.com>
>> Reviewed-by: Mark Tinguely <tinguely@sgi.com>
>> Reviewed-by: Christoph Hellwig <hch@lst.de>
>> Reviewed-by: Dave Chinner <dchinner@redhat.com>
>>
>> ---
>>   fs/xfs/xfs_file.c |   90 +++++++++++++++++++++++++++++++++++++++++++++++------
>>   1 files changed, 80 insertions(+), 10 deletions(-)
>>
>> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
>> index 15acd4d..1b83549 100644
>> --- a/fs/xfs/xfs_file.c
>> +++ b/fs/xfs/xfs_file.c
>> @@ -1296,9 +1296,9 @@ xfs_seek_hole(
>>   	struct xfs_inode	*ip = XFS_I(inode);
>>   	struct xfs_mount	*mp = ip->i_mount;
>>   	loff_t			uninitialized_var(offset);
>> -	loff_t			holeoff;
>>   	xfs_fsize_t		isize;
>>   	xfs_fileoff_t		fsbno;
>> +	xfs_filblks_t		end;
>>   	uint			lock;
>>   	int			error;
>>   
>> @@ -1314,20 +1314,90 @@ xfs_seek_hole(
>>   	}
>>   
>>   	fsbno = XFS_B_TO_FSBT(mp, start);
>> -	error = xfs_bmap_first_unused(NULL, ip, 1, &fsbno, XFS_DATA_FORK);
>> -	if (error)
>> -		goto out_unlock;
>> +	end = XFS_B_TO_FSB(mp, isize);
>> +
>> +	for (;;) {
>> +		struct xfs_bmbt_irec	map[2];
>> +		int			nmap = 2;
>> +
>> +		error = xfs_bmapi_read(ip, fsbno, end - fsbno, map, &nmap,
>> +				       XFS_BMAPI_ENTIRE);
>> +		if (error)
>> +			goto out_unlock;
>> +
>> +		/* No extents at given offset, must be beyond EOF */
>> +		if (nmap == 0) {
>> +			error = ENXIO;
>> +			goto out_unlock;
>> +		}
>>   
>> -	holeoff = XFS_FSB_TO_B(mp, fsbno);
>> -	if (holeoff <= start)
>>   		offset = start;
>> -	else {
>> +		/* Landed in a hole, return */
>> +		if (map[0].br_startblock == HOLESTARTBLOCK)
>> +			break;
>> +		else {
>> +			/*
>> +			 * Landed in an unwritten extent, try to lookup page
>> +			 * cache to find holes.
>> +			 */
> Laned in a data extent is more correct here.
>
>> +			if (map[0].br_state == XFS_EXT_UNWRITTEN ||
>> +			    isnullstartblock(map[0].br_startblock)) {
>> +				/* Probing page cache start from offset */
>> +				if (xfs_find_get_desired_pgoff(inode, &map[0],
>> +							HOLE_OFF, &offset))
>> +					break;
>> +			}
> Same logic changes as previous patch:
>
> 		if (map[0].br_startblock == HOLESTARTBLOCK)
> 			break;
> 		else if (map[0].br_state == XFS_EXT_UNWRITTEN) {
> 			ASSERT(!isnullstartblock(map[0].br_startblock));
>
> 			/* Probing page cache start from offset */
> 			if (xfs_find_get_desired_pgoff(inode, &map[0],
> 						HOLE_OFF, &offset))
> 				break;
> 		} else {
> 			.....
>
>>   		/*
>> -		 * xfs_bmap_first_unused() could return a value bigger than
>> -		 * isize if there are no more holes past the supplied offset.
>> +		 * Both mappings contains data, proceed to the next round of
>> +		 * search if the current reading offset not beyond or hit EOF.
>>   		 */
>> -		offset = min_t(loff_t, holeoff, isize);
>> +		fsbno = map[1].br_startoff + map[1].br_blockcount;
>> +		start = XFS_FSB_TO_B(mp, fsbno);
>> +		if (start >= isize) {
>> +			offset = isize;
>> +			break;
>> +		}
> And that check can move to the start of the loop, too.
Thanks for a comprehensive review, I'll fix them according to your comments.

Thanks,
-Jeff
//
>
> Cheers,
>
> Dave.


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