Re: [RFC PATCH v2 3/5] mm: Make swap_readpage() for SWP_FS_OPS use ->direct_IO() not ->readpage()

Matthew Wilcox
2021-08-12T21:26:03Z

On Thu, Aug 12, 2021 at 09:22:24PM +0100, David Howells wrote:
> +++ b/include/linux/fs.h
> @@ -336,6 +336,7 @@ struct kiocb {
> union {
> unsigned int ki_cookie; /* for ->iopoll */
> struct wait_page_queue *ki_waitq; /* for async buffered IO */
> + struct page *ki_swap_page; /* For swapfile_read/write */

Nice idea.

> +static void __swapfile_read_complete(struct kiocb *iocb, long ret, long ret2)

I would make this take a struct page * and just one 'ret'.

> +{
> + struct page *page = iocb->ki_swap_page;
> +
> + if (ret == PAGE_SIZE) {

page_size(page)?

> + kiocb.ki_pos = page_file_offset(page);

We talked about swap_file_pos(), right?

> + ret = swap_file->f_mapping->a_ops->direct_IO(&kiocb, &to);
> +
> + __swapfile_read_complete(&kiocb, ret, 0);
> + return (ret > 0) ? 0 : ret;

What if it returns a short read?

> +static int swapfile_read(struct swap_info_struct *sis, struct page *page,
> + bool synchronous)
> +{
> + struct swapfile_kiocb *ki;
> + struct file *swap_file = sis->swap_file;
> + struct bio_vec bv = {
> + .bv_page = page,
> + .bv_len = thp_size(page),
> + .bv_offset = 0
> + };
> + struct iov_iter to;
> + int ret;
> +
> + if (synchronous)
> + return swapfile_read_sync(sis, page);

Seems a shame to set up the bio_vec and iov_iter twice. Maybe call:

iov_iter_bvec(&to, READ, &bv, 1, thp_size(page));

before swapfile_read_sync() and pass a pointer to 'to' to
swapfile_read_sync?