Re: [PATCH 1/2] iomap: make buffered writes work with RWF_DONTCACHE

[Jens Axboe <axboe@kernel.dk>]

On 2/3/25 10:19 AM, Darrick J. Wong wrote:
> On Mon, Feb 03, 2025 at 09:32:38AM -0700, Jens Axboe wrote:
>> Add iomap buffered write support for RWF_DONTCACHE. If RWF_DONTCACHE is
>> set for a write, mark the folios being written as uncached. Then
>> writeback completion will drop the pages. The write_iter handler simply
>> kicks off writeback for the pages, and writeback completion will take
>> care of the rest.
>>
>> This still needs the user of the iomap buffered write helpers to call
>> folio_end_dropbehind_write() upon successful issue of the writes.
> 
> I thought iomap calls folio_end_writeback, which cares of that?  So xfs
> doesn't itself have to call folio_end_dropbehind_write?

Yep it does, stale commit message! I'll fix it up and send out a v2.

>>  fs/iomap/buffered-io.c | 4 ++++
>>  include/linux/iomap.h  | 1 +
>>  2 files changed, 5 insertions(+)
>>
>> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
>> index d303e6c8900c..ea863c3cf510 100644
>> --- a/fs/iomap/buffered-io.c
>> +++ b/fs/iomap/buffered-io.c
>> @@ -603,6 +603,8 @@ struct folio *iomap_get_folio(struct iomap_iter *iter, loff_t pos, size_t len)
>>  
>>  	if (iter->flags & IOMAP_NOWAIT)
>>  		fgp |= FGP_NOWAIT;
>> +	if (iter->flags & IOMAP_DONTCACHE)
>> +		fgp |= FGP_DONTCACHE;
>>  	fgp |= fgf_set_order(len);
>>  
>>  	return __filemap_get_folio(iter->inode->i_mapping, pos >> PAGE_SHIFT,
>> @@ -1034,6 +1036,8 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *i,
>>  
>>  	if (iocb->ki_flags & IOCB_NOWAIT)
>>  		iter.flags |= IOMAP_NOWAIT;
>> +	if (iocb->ki_flags & IOCB_DONTCACHE)
>> +		iter.flags |= IOMAP_DONTCACHE;
>>  
>>  	while ((ret = iomap_iter(&iter, ops)) > 0)
>>  		iter.processed = iomap_write_iter(&iter, i);
>> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
>> index 75bf54e76f3b..26b0dbe23e62 100644
>> --- a/include/linux/iomap.h
>> +++ b/include/linux/iomap.h
>> @@ -183,6 +183,7 @@ struct iomap_folio_ops {
>>  #define IOMAP_DAX		0
>>  #endif /* CONFIG_FS_DAX */
>>  #define IOMAP_ATOMIC		(1 << 9)
>> +#define IOMAP_DONTCACHE		(1 << 10)
> 
> This needs a mention in the iomap documentation.  If the patch below
> accurately summarizes what it does nowadays, then you can add it to the
> series with a:

Thanks Darrick, I'll add that and your SOB as well.

-- 
Jens Axboe