Re: [PATCH 02/23] MM: extend block-plugging to cover all swap reads with read-ahead

[Christoph Hellwig]

On Mon, Jan 24, 2022 at 02:48:32PM +1100, NeilBrown wrote:
> Code that does swap read-ahead uses blk_start_plug() and
> blk_finish_plug() to allow lower levels to combine multiple read-ahead
> pages into a single request, but calls blk_finish_plug() *before*
> submitting the original (non-ahead) read request.
> This missed an opportunity to combine read requests.
> 
> This patch moves the blk_finish_plug to *after* all the reads.
> This will likely combine the primary read with some of the "ahead"
> reads, and that may slightly increase the latency of that read, but it
> should more than make up for this by making more efficient use of the
> storage path.
> 
> The patch mostly makes the code look more consistent.  Performance
> change is unlikely to be noticeable.

Looks good:

Reviewed-by: Christoph Hellwig <hch@xxxxxx>

> Fixes-no-auto-backport: 3fb5c298b04e ("swap: allow swap readahead to be merged")

Is this really a thing?