Re: [PATCH 1/2] filemap: Convert generic_perform_write() to support large folios

[Christoph Hellwig <hch@lst.de>]

On Wed, Jun 12, 2024 at 08:41:01AM +0700, Shaun Tancheff wrote:
> On 6/11/24 23:13, Christoph Hellwig wrote:
>
>> On Tue, Jun 11, 2024 at 05:47:12PM +0700, Shaun Tancheff wrote:
>>>>    	const struct address_space_operations *a_ops = mapping->a_ops;
>>>> +	size_t chunk = mapping_max_folio_size(mapping);
>>> Better to default chunk to PAGE_SIZE for backward compat
>>> +       size_t chunk = PAGE_SIZE;
>>>
>>>>    	long status = 0;
>>>>    	ssize_t written = 0;
>>>>    
>>> Have fs opt in to large folio support:
>>>
>>> +       if (mapping_large_folio_support(mapping))
>>> +               chunk = PAGE_SIZE << MAX_PAGECACHE_ORDER;
>> I don't think you've actually read the code, have you?
>
> I checked from 6.6 to linux-next with this patch and my ext4 VM does not boot without the opt-in.

Please take a look at the definition of mapping_max_folio_size,
which is called above in the quoted patch.