Re: [PATCH 12/13] MM: use AIO/DIO for reads from SWP_FS_OPS swap-space

From: Christoph Hellwig
Date: Tue Nov 16 2021 - 03:32:08 EST

On Tue, Nov 16, 2021 at 01:44:04PM +1100, NeilBrown wrote:
> When pages a read from SWP_FS_OPS swap-space, the reads are submitted as
> separate reads for each page. This is generally less efficient than
> larger reads.
> We can use the block-plugging infrastructure to delay submitting the
> read request until multiple contigious pages have been collected. This
> requires using ->direct_IO to submit the read (as ->readpages isn't
> suitable for swap).

Abusing the block code here seems little ugly. Also this won't
compile if CONFIG_BLOCK is not set, will it?

What is the problem with just batching up manually?

> + /* nofs needs as ->direct_IO may take the same mutex it takes for write */

Overly long line.