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

[Matthew Wilcox <willy@infradead.org>]

On Mon, May 27, 2024 at 06:36:08PM +0200, Christoph Hellwig wrote:
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> 
> Modelled after the loop in iomap_write_iter(), copy larger chunks from
> userspace if the filesystem has created large folios.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> [hch: use mapping_max_folio_size to keep supporting file systems that do
>  not support large folios]
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Yup, this still makes sense to me.

Could you remind me why we need to call flush_dcache_folio() in
generic_perform_write() while we don't in iomap_write_iter()?

>  		if (mapping_writably_mapped(mapping))
> -			flush_dcache_page(page);
> +			flush_dcache_folio(folio);

(i'm not talking about this one)

> -		copied = copy_page_from_iter_atomic(page, offset, bytes, i);
> -		flush_dcache_page(page);
> +		copied = copy_folio_from_iter_atomic(folio, offset, bytes, i);
> +		flush_dcache_folio(folio);

(this one has no equivalent in iomap)

>  		status = a_ops->write_end(file, mapping, pos, bytes, copied,
>  						page, fsdata);