Re: Re：[PATCH] mm: vmpressure: simplify pressure ratio calculation

[Michal Hocko <mhocko@kernel.org>]

On Tue 04-07-17 21:43:39, zbestahu wrote:
> Michal wrote:
> > > the existing percent
> > > calculation using scale should be about rounding to intege, it
> > > seems to be redundant, we can calculate it directly just like
> > > "pressure = not_relaimed * 100 / scanned", no rounding issue. And
> > > it's also better because of saving several arithmetic operations.
> 
> > and you haven't explained why that change is so much better to change
> > the behavior.
> 
> it removes 3 below arithmetic instructions so it should be running faster.
> add: scanned + reclaimed
> mul: scale * reclaimed
> udiv: reclaimed * scale /scanned

That part is clear from the diff... What is not clear from the diff is
your motivation. This path is not hot (we are in the reclaim which is a
slow path) and few extra instructions are acceptable. Sure we can
optimize it if the resulting code is working as expected. What I am
asking (obviously unsuccessfully) is to describe _why_ it is better.
This is a requirement for _each patch_. We are not changing the code
"just because I like it more that way".
-- 
Michal Hocko
SUSE Labs

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