Re: [PATCH v3 8/8] iomap: Copy larger chunks from userspace

[Christoph Hellwig <hch@infradead.org>]

On Mon, Jun 12, 2023 at 09:39:10PM +0100, Matthew Wilcox (Oracle) wrote:
> If we have a large folio, we can copy in larger chunks than PAGE_SIZE.
> Start at the maximum page cache size and shrink by half every time we
> hit the "we are short on memory" problem.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>  fs/iomap/buffered-io.c | 22 +++++++++++++---------
>  1 file changed, 13 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index a5d62c9640cf..818dc350ffc5 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -768,6 +768,7 @@ static size_t iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
>  static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
>  {
>  	loff_t length = iomap_length(iter);
> +	size_t chunk = PAGE_SIZE << MAX_PAGECACHE_ORDER;

This could overflow if the chunk size ends up bigger than 4GB, but
I guess that's mostly theoretical.

> -		copied = copy_page_from_iter_atomic(page, offset, bytes, i);
> +		copied = copy_page_from_iter_atomic(&folio->page, offset, bytes, i);

Would be nice t avoid the overly long line here

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>