linux-kernel - Re: [PATCH v10 12/14] mm: multi-gen LRU: debugfs interface

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Date:   Fri, 15 Apr 2022 21:20:24 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Stephen Rothwell <sfr@...hwell.id.au>,
        Linux-MM <linux-mm@...ck.org>, Andi Kleen <ak@...ux.intel.com>,
        Aneesh Kumar <aneesh.kumar@...ux.ibm.com>,
        Barry Song <21cnbao@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Hillf Danton <hdanton@...a.com>, Jens Axboe <axboe@...nel.dk>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Michael Larabel <Michael@...haellarabel.com>,
        Michal Hocko <mhocko@...nel.org>,
        Mike Rapoport <rppt@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Will Deacon <will@...nel.org>,
        Ying Huang <ying.huang@...el.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Kernel Page Reclaim v2 <page-reclaim@...gle.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Brian Geffon <bgeffon@...gle.com>,
        Jan Alexander Steffens <heftig@...hlinux.org>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Steven Barrett <steven@...uorix.net>,
        Suleiman Souhlal <suleiman@...gle.com>,
        Daniel Byrne <djbyrne@....edu>,
        Donald Carr <d@...os-reins.com>,
        Holger Hoffstätte 
        <holger@...lied-asynchrony.com>,
        Konstantin Kharlamov <Hi-Angel@...dex.ru>,
        Shuang Zhai <szhai2@...rochester.edu>,
        Sofia Trinh <sofia.trinh@....works>,
        Vaibhav Jain <vaibhav@...ux.ibm.com>
Subject: Re: [PATCH v10 12/14] mm: multi-gen LRU: debugfs interface

On Fri, 15 Apr 2022 18:03:16 -0600 Yu Zhao <yuzhao@...gle.com> wrote:

> > Presumably sysfs is the place.  Fully documented and with usage
> > examples in the changelog so we can carefully review the proposed
> > extensions to Linux's ABI.  Extensions which must be maintained
> > unchanged for all time.
> 
> Eventually, yes. There still is a long way to go. Rest assured, this
> is something Google will keep investing resources on.

So.  The plan is to put these interfaces in debugfs for now, with a
view to migrating stabilized interfaces into sysfs (or procfs or
whatever) once end-user requirements and use cases are better
understood?

If so, that sounds totally great to me.  But it should have been in
the darn changelog!  This is the sort of thing which we care about most
keenly.

It would be helpful for reviewers to understand the proposed timeline
for this process, because the entire feature isn't really real until
this is completed, is it?  I do think we should get this nailed down
relatively rapidly, otherwise people will be reluctant to invest much
into a moving target.

And I must say, I see dissonance between the overall maturity of the
feature as described in these emails versus the immaturity of these
userspace control interfaces.  What's happening there?