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From:   "Huang, Ying" <ying.huang@intel.com>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Arjan Van De Ven <arjan@linux.intel.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Vlastimil Babka <vbabka@suse.cz>,
        David Hildenbrand <david@redhat.com>,
        Johannes Weiner <jweiner@redhat.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Michal Hocko <mhocko@suse.com>,
        Pavel Tatashin <pasha.tatashin@soleen.com>,
        Matthew Wilcox <willy@infradead.org>,
        Christoph Lameter <cl@linux.com>
Subject: Re: [PATCH 00/10] mm: PCP high auto-tuning
References: <20230920061856.257597-1-ying.huang@intel.com>
        <20230920094118.8b8f739125c6aede17c627e0@linux-foundation.org>
        <87leczwt1o.fsf@yhuang6-desk2.ccr.corp.intel.com>
        <20230921084617.b1129a46de247e4a6f0098af@linux-foundation.org>
Date:   Fri, 22 Sep 2023 08:33:52 +0800
In-Reply-To: <20230921084617.b1129a46de247e4a6f0098af@linux-foundation.org>
        (Andrew Morton's message of "Thu, 21 Sep 2023 08:46:17 -0700")
Message-ID: <87h6nnvyfj.fsf@yhuang6-desk2.ccr.corp.intel.com>
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Andrew Morton <akpm@linux-foundation.org> writes:

> On Thu, 21 Sep 2023 21:32:35 +0800 "Huang, Ying" <ying.huang@intel.com> 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@techsingularity.net/
>> 
>> "
>> 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.

Sure.  Will add document about auto-tuning behavior in the above
document.

--
Best Regards,
Huang, Ying