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From: Stefan Roesch <[email protected]>
To: Dave Chinner <[email protected]>
Cc: [email protected], [email protected], [email protected],
	[email protected], [email protected]
Subject: Re: [RFC PATCH v1 06/18] xfs: add iomap async buffered write support
Date: Thu, 28 Apr 2022 13:03:49 -0700	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>



On 4/26/22 3:54 PM, Dave Chinner wrote:
> On Tue, Apr 26, 2022 at 10:43:23AM -0700, Stefan Roesch wrote:
>> This adds the async buffered write support to the iomap layer of XFS. If
>> a lock cannot be acquired or additional reads need to be performed, the
>> request will return -EAGAIN in case this is an async buffered write request.
>>
>> Signed-off-by: Stefan Roesch <[email protected]>
>> ---
>>  fs/xfs/xfs_iomap.c | 33 +++++++++++++++++++++++++++++++--
>>  1 file changed, 31 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
>> index e552ce541ec2..80b6c48e88af 100644
>> --- a/fs/xfs/xfs_iomap.c
>> +++ b/fs/xfs/xfs_iomap.c
>> @@ -881,18 +881,28 @@ xfs_buffered_write_iomap_begin(
>>  	bool			eof = false, cow_eof = false, shared = false;
>>  	int			allocfork = XFS_DATA_FORK;
>>  	int			error = 0;
>> +	bool			no_wait = (flags & IOMAP_NOWAIT);
>>  
>>  	if (xfs_is_shutdown(mp))
>>  		return -EIO;
>>  
>>  	/* we can't use delayed allocations when using extent size hints */
>> -	if (xfs_get_extsz_hint(ip))
>> +	if (xfs_get_extsz_hint(ip)) {
>> +		if (no_wait)
>> +			return -EAGAIN;
>> +
>>  		return xfs_direct_write_iomap_begin(inode, offset, count,
>>  				flags, iomap, srcmap);
> 
> Why can't we do IOMAP_NOWAIT allocation here?
> xfs_direct_write_iomap_begin() supports IOMAP_NOWAIT semantics just
> fine - that's what the direct IO path uses...

I'll make that change in the next version.
> 
>> +	}
>>  
>>  	ASSERT(!XFS_IS_REALTIME_INODE(ip));
>>  
>> -	xfs_ilock(ip, XFS_ILOCK_EXCL);
>> +	if (no_wait) {
>> +		if (!xfs_ilock_nowait(ip, XFS_ILOCK_EXCL))
>> +			return -EAGAIN;
>> +	} else {
>> +		xfs_ilock(ip, XFS_ILOCK_EXCL);
>> +	}
> 
> handled by xfs_ilock_for_iomap().

The helper xfs_ilock_for_iomap cannot be used for this purpose. The function
xfs_ilock_for_iomap tries to deduce the lock mode. For the function xfs_file_buffered_write()
the lock mode must be exclusive. However this is not always the case when the
helper xfs_ilock_for_iomap is used. There are cases where xfs_is_cow_inode(() is not
true.

I'll add a new helper that will be used here.

>>  
>>  	if (XFS_IS_CORRUPT(mp, !xfs_ifork_has_extents(&ip->i_df)) ||
>>  	    XFS_TEST_ERROR(false, mp, XFS_ERRTAG_BMAPIFORMAT)) {
>> @@ -902,6 +912,11 @@ xfs_buffered_write_iomap_begin(
>>  
>>  	XFS_STATS_INC(mp, xs_blk_mapw);
>>  
>> +	if (no_wait && xfs_need_iread_extents(XFS_IFORK_PTR(ip, XFS_DATA_FORK))) {
>> +		error = -EAGAIN;
>> +		goto out_unlock;
>> +	}
>> +
> 
> Also handled by xfs_ilock_for_iomap().

I'll remove this check with the next version.

> 
>>  	error = xfs_iread_extents(NULL, ip, XFS_DATA_FORK);
>>  	if (error)
>>  		goto out_unlock;
>> @@ -933,6 +948,10 @@ xfs_buffered_write_iomap_begin(
>>  	if (xfs_is_cow_inode(ip)) {
>>  		if (!ip->i_cowfp) {
>>  			ASSERT(!xfs_is_reflink_inode(ip));
>> +			if (no_wait) {
>> +				error = -EAGAIN;
>> +				goto out_unlock;
>> +			}
>>  			xfs_ifork_init_cow(ip);
>>  		}
> 
> Also handled by xfs_ilock_for_iomap().
> 

I'll remove this check with the next version.


>>  		cow_eof = !xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb,
>> @@ -956,6 +975,11 @@ xfs_buffered_write_iomap_begin(
>>  			goto found_imap;
>>  		}
>>  
>> +		if (no_wait) {
>> +			error = -EAGAIN;
>> +			goto out_unlock;
>> +		}
>> +
> 
> Won't get here because this is COW path, and xfs_ilock_for_iomap()
> handles returning -EAGAIN for that case.

I'll remove this check with the next version.

> 
>>  		xfs_trim_extent(&imap, offset_fsb, end_fsb - offset_fsb);
>>  
>>  		/* Trim the mapping to the nearest shared extent boundary. */
>> @@ -993,6 +1017,11 @@ xfs_buffered_write_iomap_begin(
>>  			allocfork = XFS_COW_FORK;
>>  	}
>>  
>> +	if (no_wait) {
>> +		error = -EAGAIN;
>> +		goto out_unlock;
>> +	}
> 
> Why? Delayed allocation doesn't block...

I'll remove this check with the next version.

> 
> Cheers,
> 
> Dave.
> 

  reply	other threads:[~2022-04-28 20:04 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-26 17:43 [RFC PATCH v1 00/18] io-uring/xfs: support async buffered writes Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 01/18] block: add check for async buffered writes to generic_write_checks Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 02/18] mm: add FGP_ATOMIC flag to __filemap_get_folio() Stefan Roesch
2022-04-26 19:06   ` Matthew Wilcox
2022-04-28 19:54     ` Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 03/18] iomap: add iomap_page_create_gfp to allocate iomap_pages Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 04/18] iomap: use iomap_page_create_gfp() in __iomap_write_begin Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 05/18] iomap: add async buffered write support Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 06/18] xfs: add iomap " Stefan Roesch
2022-04-26 22:54   ` Dave Chinner
2022-04-28 20:03     ` Stefan Roesch [this message]
2022-04-28 21:44       ` Dave Chinner
2022-04-26 17:43 ` [RFC PATCH v1 07/18] fs: split off need_remove_file_privs() do_remove_file_privs() Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 08/18] fs: split off need_file_update_time and do_file_update_time Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 09/18] fs: add pending file update time flag Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 10/18] xfs: Enable async write file modification handling Stefan Roesch
2022-04-26 22:55   ` Dave Chinner
2022-04-27 12:07   ` Christian Brauner
2022-04-26 17:43 ` [RFC PATCH v1 11/18] xfs: add async buffered write support Stefan Roesch
2022-04-26 22:56   ` Dave Chinner
2022-04-28 19:58     ` Stefan Roesch
2022-04-28 21:54       ` Dave Chinner
2022-05-02 21:21         ` Stefan Roesch
2022-05-06  9:29           ` Dave Chinner
2022-05-09 19:32             ` Stefan Roesch
2022-05-09 23:24               ` Dave Chinner
2022-05-09 23:44                 ` Darrick J. Wong
2022-05-10  1:12                   ` Dave Chinner
2022-05-10  6:47                     ` Christoph Hellwig
2022-05-16  2:24                       ` Dave Chinner
2022-05-16 13:39                         ` Christoph Hellwig
2022-04-26 17:43 ` [RFC PATCH v1 12/18] io_uring: add support for async buffered writes Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 13/18] io_uring: add tracepoint for short writes Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 14/18] sched: add new fields to task_struct Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 15/18] mm: support write throttling for async buffered writes Stefan Roesch
2022-04-28 17:47   ` Jan Kara
2022-04-28 20:16     ` Stefan Roesch
2022-05-10  9:50       ` Jan Kara
2022-05-10 20:16         ` Stefan Roesch
2022-05-11 10:38           ` Jan Kara
2022-05-13 18:57             ` Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 16/18] iomap: User " Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 17/18] io_uring: support write " Stefan Roesch
2022-04-26 17:43 ` [RFC PATCH v1 18/18] xfs: enable async buffered write support Stefan Roesch
2022-04-26 22:37 ` [RFC PATCH v1 00/18] io-uring/xfs: support async buffered writes Dave Chinner

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