Re: [PATCH 00/10] mm: PCP high auto-tuning

[Andrew Morton]

On Thu, 21 Sep 2023 21:32:35 +0800 "Huang, Ying" <ying.huang@xxxxxxxxx> wrote:

> >   : It's possible that PCP high auto-tuning doesn't work well for some
> >   : workloads.  So, when PCP high is tuned by hand via the sysctl knob,
> >   : the auto-tuning will be disabled.  The PCP high set by hand will be
> >   : used instead.
> >
> >   Is it a bit hacky to disable autotuning when the user alters
> >   pcp-high?  Would it be cleaner to have a separate on/off knob for
> >   autotuning?
> 
> This was suggested by Mel Gormon,
> 
> https://lore.kernel.org/linux-mm/20230714140710.5xbesq6xguhcbyvi@xxxxxxxxxxxxxxxxxxx/
> 
> "
> I'm not opposed to having an adaptive pcp->high in concept. I think it would
> be best to disable adaptive tuning if percpu_pagelist_high_fraction is set
> though. I expect that users of that tunable are rare and that if it *is*
> used that there is a very good reason for it.
> "
> 
> Do you think that this is reasonable?

I suppose so, if it's documented!

Documentation/admin-guide/sysctl/vm.rst describes
percpu_pagelist_high_fraction.