Re: [PATCH v3 04/12] fuse: support large folios for writethrough writes

[Jeff Layton <jlayton@kernel.org>]

On Fri, 2024-12-13 at 14:18 -0800, Joanne Koong wrote:
> Add support for folios larger than one page size for writethrough
> writes.
> 
> Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
> ---
>  fs/fuse/file.c | 19 ++++++++++++-------
>  1 file changed, 12 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index c041bb328203..84e39426862a 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -1135,6 +1135,7 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
>  				     struct iov_iter *ii, loff_t pos,
>  				     unsigned int max_pages)
>  {
> +	size_t max_folio_size = mapping_max_folio_size(mapping);
>  	struct fuse_args_pages *ap = &ia->ap;
>  	struct fuse_conn *fc = get_fuse_conn(mapping->host);
>  	unsigned offset = pos & (PAGE_SIZE - 1);
> @@ -1146,17 +1147,17 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
>  	num = min(num, max_pages << PAGE_SHIFT);
>  
>  	ap->args.in_pages = true;
> -	ap->descs[0].offset = offset;
>  
>  	while (num) {
>  		size_t tmp;
>  		struct folio *folio;
>  		pgoff_t index = pos >> PAGE_SHIFT;
> -		unsigned int bytes = min(PAGE_SIZE - offset, num);
> +		unsigned int bytes;
> +		unsigned int folio_offset;
>  
>   again:
>  		err = -EFAULT;
> -		if (fault_in_iov_iter_readable(ii, bytes))
> +		if (fault_in_iov_iter_readable(ii, max_folio_size) == max_folio_size)
>  			break;
>  
>  		folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
> @@ -1169,7 +1170,10 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
>  		if (mapping_writably_mapped(mapping))
>  			flush_dcache_folio(folio);
>  
> -		tmp = copy_folio_from_iter_atomic(folio, offset, bytes, ii);
> +		folio_offset = ((index - folio->index) << PAGE_SHIFT) + offset;
> +		bytes = min(folio_size(folio) - folio_offset, num);
> +
> +		tmp = copy_folio_from_iter_atomic(folio, folio_offset, bytes, ii);

Just to save someone else going down the same rabbit hole:

copy_folio_from_iter_atomic() is defined as:

static inline size_t copy_folio_from_iter_atomic(struct folio *folio,
                size_t offset, size_t bytes, struct iov_iter *i)
{
        return copy_page_from_iter_atomic(&folio->page, offset, bytes, i);
}

...which _looks_ sort of like it's not fully baked yet and can't handle
a large folio, but it turns out that copy_page_from_iter_atomic() can
handle compound pages, so I think this is actually OK. Whew!


>  		flush_dcache_folio(folio);
>  
>  		if (!tmp) {
> @@ -1180,6 +1184,7 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
>  
>  		err = 0;
>  		ap->folios[ap->num_folios] = folio;
> +		ap->descs[ap->num_folios].offset = folio_offset;
>  		ap->descs[ap->num_folios].length = tmp;
>  		ap->num_folios++;
>  
> @@ -1187,11 +1192,11 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
>  		pos += tmp;
>  		num -= tmp;
>  		offset += tmp;
> -		if (offset == PAGE_SIZE)
> +		if (offset == folio_size(folio))
>  			offset = 0;
>  
> -		/* If we copied full page, mark it uptodate */
> -		if (tmp == PAGE_SIZE)
> +		/* If we copied full folio, mark it uptodate */
> +		if (tmp == folio_size(folio))
>  			folio_mark_uptodate(folio);
>  
>  		if (folio_test_uptodate(folio)) {

-- 
Jeff Layton <jlayton@kernel.org>