Re: [PATCH 03/13] bcache: inherit the optimal I/O size

From: Christoph Hellwig
Date: Mon Sep 21 2020 - 10:00:18 EST

On Mon, Sep 21, 2020 at 05:54:59PM +0800, Coly Li wrote:
> I am not sure whether virtual bcache device's optimal request size can
> be simply set like this.
> Most of time inherit backing device's optimal request size is fine, but
> there are two exceptions,
> - Read request hits on cache device
> - User sets sequential_cuttoff as 0, all writing may go into cache
> device firstly.
> For the above two conditions, all I/Os goes into cache device, using
> optimal request size of backing device might be improper.
> Just a guess, is it OK to set the optimal request size of the virtual
> bcache device as the least common multiple of cache device's and backing
> device's optimal request sizes ?

Well, if the optimal I/O size is wrong, the read ahead size also is
wrong. Can we just drop the setting?