Re: [PATCH v2 4/6] iomap: correct the dirty length in page mkwrite

[Zhang Yi <yi.zhang@huaweicloud.com>]

On 2024/8/13 0:45, Darrick J. Wong wrote:
> On Mon, Aug 12, 2024 at 08:11:57PM +0800, Zhang Yi wrote:
>> From: Zhang Yi <yi.zhang@huawei.com>
>>
>> When doing page mkwrite, iomap_folio_mkwrite_iter() dirty the entire
>> folio by folio_mark_dirty() even the map length is shorter than one
>> folio. However, on the filesystem with more than one blocks per folio,
>> we'd better to only set counterpart block's dirty bit according to
>> iomap_length(), so open code folio_mark_dirty() and pass the correct
>> length.
>>
>> Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
>> ---
>>  fs/iomap/buffered-io.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
>> index 79031b7517e5..ac762de9a27f 100644
>> --- a/fs/iomap/buffered-io.c
>> +++ b/fs/iomap/buffered-io.c
>> @@ -1492,7 +1492,10 @@ static loff_t iomap_folio_mkwrite_iter(struct iomap_iter *iter,
>>  		block_commit_write(&folio->page, 0, length);
>>  	} else {
>>  		WARN_ON_ONCE(!folio_test_uptodate(folio));
>> -		folio_mark_dirty(folio);
>> +
>> +		ifs_alloc(iter->inode, folio, 0);
>> +		iomap_set_range_dirty(folio, 0, length);
>> +		filemap_dirty_folio(iter->inode->i_mapping, folio);
> 
> Is it correct to be doing a lot more work by changing folio_mark_dirty
> to filemap_dirty_folio?  Now pagefaults call __mark_inode_dirty which
> they did not before.  Also, the folio itself must be marked dirty if any
> of the ifs bitmap is marked dirty, so I don't understand the change
> here.
> 

This change is just open code iomap_dirty_folio() and correct the length
that passing to iomap_set_range_dirty().

bool iomap_dirty_folio(struct address_space *mapping, struct folio *folio)
{
	struct inode *inode = mapping->host;
	size_t len = folio_size(folio);
...
	ifs_alloc(inode, folio, 0);
	iomap_set_range_dirty(folio, 0, len);
	return filemap_dirty_folio(mapping, folio);
}

Before this change, the code also call filemap_dirty_folio() (though
folio_mark_dirty()->iomap_dirty_folio()->filemap_dirty_folio()), so it call
__mark_inode_dirty() too. After this change, filemap_dirty_folio()->
folio_test_set_dirty() will mark the folio dirty. Hence there is no
difference between the two points you mentioned. Am I missing something?

Thanks,
Yi.

> 
>>  	}
>>  
>>  	return length;
>> -- 
>> 2.39.2
>>
>>