Re: [PATCH v2 1/4] blk-iocost: charge flushes as pageless random writes

[Tejun Heo]

On Mon, Sep 21, 2026 at 12:06:11AM -0700, Christoph Hellwig wrote:
> On Sat, Sep 19, 2026 at 04:59:51AM -1000, Tejun Heo wrote:
> > Hello, Tao.
> > Pricing a flush as a random write, or as a page where that comes out to
> > zero, is as arbitrary as pricing it at zero,
> 
> No, it absolutely is not.  For any flush that actually makes here it
> is extremely expensive, and 0 is the wrongest possible value.  Even
> batching does not change that, as batching is not actually effective
> in any normal file system workload.

I see. I don't think the default value matters all that much given how crude
a tool the default model is. We can set it to a page. I don't think we
should impose it on existing users that are configuring custom models.

Thanks.

-- 
tejun