linux-kernel - Re: [RFC PATCH 0/2] Add predictive memory reclamation and compaction

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Date:   Wed, 21 Aug 2019 16:06:32 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Khalid Aziz <khalid.aziz@...cle.com>
Cc:     akpm@...ux-foundation.org, vbabka@...e.cz,
        mgorman@...hsingularity.net, dan.j.williams@...el.com,
        osalvador@...e.de, richard.weiyang@...il.com, hannes@...xchg.org,
        arunks@...eaurora.org, rppt@...ux.vnet.ibm.com, jgg@...pe.ca,
        amir73il@...il.com, alexander.h.duyck@...ux.intel.com,
        linux-mm@...ck.org, linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] Add predictive memory reclamation and compaction

On Thu 15-08-19 14:51:04, Khalid Aziz wrote:
> Hi Michal,
> 
> The smarts for tuning these knobs can be implemented in userspace and
> more knobs added to allow for what is missing today, but we get back to
> the same issue as before. That does nothing to make kernel self-tuning
> and adds possibly even more knobs to userspace. Something so fundamental
> to kernel memory management as making free pages available when they are
> needed really should be taken care of in the kernel itself. Moving it to
> userspace just means the kernel is hobbled unless one installs and tunes
> a userspace package correctly.

>From my past experience the existing autotunig works mostly ok for a
vast variety of workloads. A more clever tuning is possible and people
are doing that already. Especially for cases when the machine is heavily
overcommited. There are different ways to achieve that. Your new
in-kernel auto tuning would have to be tested on a large variety of
workloads to be proven and riskless. So I am quite skeptical to be
honest.

Therefore I would really focus on discussing whether we have sufficient
APIs to tune the kernel to do the right thing when needed. That requires
to identify gaps in that area.
-- 
Michal Hocko
SUSE Labs