[Cluster-devel] [RFC v6 08/10] iomap/xfs: Eliminate the iomap_valid handler

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

On 1/18/23 16:21, Christoph Hellwig wrote:
> On Sun, Jan 15, 2023 at 09:29:58AM -0800, Darrick J. Wong wrote:
>> I don't have any objections to pulling everything except patches 8 and
>> 10 for testing this week. 
> 
> That would be great.  I now have a series to return the ERR_PTR
> from __filemap_get_folio which will cause a minor conflict, but
> I think that's easy enough for Linux to handle.
> 
>>
>> 1. Does zonefs need to revalidate mappings?  The mappings are 1:1 so I
>> don't think it does, but OTOH zone pointer management might complicate
>> that.
> 
> Adding Damien.

zonefs has a static mapping of file blocks that never changes and is fully
populated up to a file max size from mount. So zonefs is not using the
iomap_valid page operation. In fact, zonefs is not even using struct
iomap_page_ops.

> 
>> 2. How about porting the writeback iomap validation to use this
>> mechanism?  (I suspect Dave might already be working on this...)
> 
> What is "this mechanism"?  Do you mean the here removed ->iomap_valid
> ?   writeback calls into ->map_blocks for every block while under the
> folio lock, so the validation can (and for XFS currently is) done
> in that.  Moving it out into a separate method with extra indirect
> functiona call overhead and interactions between the methods seems
> like a retrograde step to me.
> 
>> 2. Do we need to revalidate mappings for directio writes?  I think the
>> answer is no (for xfs) because the ->iomap_begin call will allocate
>> whatever blocks are needed and truncate/punch/reflink block on the
>> iolock while the directio writes are pending, so you'll never end up
>> with a stale mapping.
> 
> Yes.

-- 
Damien Le Moal
Western Digital Research