From: Yu Zhao <yuzhao@google.com>
To: Mike Rapoport <rppt@kernel.org>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Johannes Weiner" <hannes@cmpxchg.org>,
"Mel Gorman" <mgorman@suse.de>,
"Michal Hocko" <mhocko@kernel.org>,
"Andi Kleen" <ak@linux.intel.com>,
"Aneesh Kumar" <aneesh.kumar@linux.ibm.com>,
"Barry Song" <21cnbao@gmail.com>,
"Catalin Marinas" <catalin.marinas@arm.com>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
"Hillf Danton" <hdanton@sina.com>, "Jens Axboe" <axboe@kernel.dk>,
"Jesse Barnes" <jsbarnes@google.com>,
"Jonathan Corbet" <corbet@lwn.net>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
"Matthew Wilcox" <willy@infradead.org>,
"Michael Larabel" <Michael@michaellarabel.com>,
"Rik van Riel" <riel@surriel.com>,
"Vlastimil Babka" <vbabka@suse.cz>,
"Will Deacon" <will@kernel.org>,
"Ying Huang" <ying.huang@intel.com>,
"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
"Kernel Page Reclaim v2" <page-reclaim@google.com>,
"the arch/x86 maintainers" <x86@kernel.org>,
"Brian Geffon" <bgeffon@google.com>,
"Jan Alexander Steffens" <heftig@archlinux.org>,
"Oleksandr Natalenko" <oleksandr@natalenko.name>,
"Steven Barrett" <steven@liquorix.net>,
"Suleiman Souhlal" <suleiman@google.com>,
"Daniel Byrne" <djbyrne@mtu.edu>,
"Donald Carr" <d@chaos-reins.com>,
"Holger Hoffstätte" <holger@applied-asynchrony.com>,
"Konstantin Kharlamov" <Hi-Angel@yandex.ru>,
"Shuang Zhai" <szhai2@cs.rochester.edu>,
"Sofia Trinh" <sofia.trinh@edi.works>
Subject: Re: [PATCH v7 12/12] mm: multigenerational LRU: documentation
Date: Wed, 23 Feb 2022 14:20:32 -0700 [thread overview]
Message-ID: <CAOUHufasp_to43QPi9y9rTtFKNBTjETzOiEQgm-3Hc6nzyziZA@mail.gmail.com> (raw)
In-Reply-To: <YhYTU3B7cdwV+YrW@kernel.org>
On Wed, Feb 23, 2022 at 3:58 AM Mike Rapoport <rppt@kernel.org> wrote:
>
> On Mon, Feb 21, 2022 at 06:47:25PM -0700, Yu Zhao wrote:
> > On Mon, Feb 21, 2022 at 2:02 AM Mike Rapoport <rppt@kernel.org> wrote:
> > >
> > > On Tue, Feb 15, 2022 at 08:22:10PM -0700, Yu Zhao wrote:
> > > > > Please consider splitting "enable" and "features" attributes.
> > > >
> > > > How about s/Features/Components/?
> > >
> > > I meant to use two attributes:
> > >
> > > /sys/kernel/mm/lru_gen/enable for the main breaker, and
> > > /sys/kernel/mm/lru_gen/features (or components) for the branch breakers
> >
> > It's a bit superfluous for my taste. I generally consider multiple
> > items to fall into the same category if they can be expressed by a
> > type of array, and I usually pack an array into a single file.
> >
> > From your last review, I gauged this would be too overloaded for your
> > taste. So I'd be happy to make the change if you think two files look
> > more intuitive from user's perspective.
>
> I do think that two attributes are more user-friendly, but I don't feel
> strongly about it.
>
> > > > > As for the descriptions, what is the user-visible effect of these features?
> > > > > How different modes of clearing the access bit are reflected in, say, GUI
> > > > > responsiveness, database TPS, or probability of OOM?
> > > >
> > > > These remain to be seen :) I just added these switches in v7, per Mel's
> > > > request from the meeting we had. These were never tested in the field.
> > >
> > > I see :)
> > >
> > > It would be nice to have a description or/and examples of user-visible
> > > effects when there will be some insight on what these features do.
> >
> > How does the following sound?
> >
> > Clearing the accessed bit in large batches can theoretically cause
> > lock contention (mmap_lock), and if it happens the 0x0002 switch can
> > disable this feature. In this case the multigenerational LRU suffers a
> > minor performance degradation.
> > Clearing the accessed bit in non-leaf page table entries was only
> > verified on Intel and AMD, and if it causes problems on other x86
> > varieties the 0x0004 switch can disable this feature. In this case the
> > multigenerational LRU suffers a negligible performance degradation.
>
> LGTM
>
> > > > > > +:Debugfs interface: ``/sys/kernel/debug/lru_gen`` has the following
> > > > >
> > > > > Is debugfs interface relevant only for datacenters?
> > > >
> > > > For the moment, yes.
> > >
> > > And what will happen if somebody uses these interfaces outside
> > > datacenters? As soon as there is a sysfs intefrace, somebody will surely
> > > play with it.
> > >
> > > I think the job schedulers might be the most important user of that
> > > interface, but the documentation should not presume it is the only user.
> >
> > Other ideas are more like brainstorming than concrete use cases, e.g.,
> > for desktop users, these interface can in theory speed up hibernation
> > (suspend to disk); for VM users, they can again in theory support auto
> > ballooning. These niches are really minor and less explored compared
> > with the data center use cases which have been dominant.
> >
> > I was hoping we could focus on the essential and take one step at a
> > time. Later on, if there is additional demand and resource, then we
> > expand to cover more use cases.
>
> Apparently I was not clear :)
>
> I didn't mean that you should describe other use-cases, I rather suggested
> to make the documentation more neutral, e.g. using "a user writes to this
> file ..." instead of "job scheduler writes to a file ...". Or maybe add a
> sentence in the beginning of the "Data centers" section, for instance:
>
> Data centers
> ------------
>
> + A representative example of multigenerational LRU users are job
> schedulers.
>
> Data centers want to optimize job scheduling (bin packing) to improve
> memory utilizations. Job schedulers need to estimate whether a server
Yes, that makes sense. Will do. Thanks.
next prev parent reply other threads:[~2022-02-23 21:20 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-08 8:18 [PATCH v7 00/12] Multigenerational LRU Framework Yu Zhao
2022-02-08 8:18 ` [PATCH v7 01/12] mm: x86, arm64: add arch_has_hw_pte_young() Yu Zhao
2022-02-08 8:24 ` Yu Zhao
2022-02-08 10:33 ` Will Deacon
2022-02-08 8:18 ` [PATCH v7 02/12] mm: x86: add CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG Yu Zhao
2022-02-08 8:27 ` Yu Zhao
2022-02-08 8:18 ` [PATCH v7 03/12] mm/vmscan.c: refactor shrink_node() Yu Zhao
2022-02-08 8:18 ` [PATCH v7 04/12] mm: multigenerational LRU: groundwork Yu Zhao
2022-02-08 8:28 ` Yu Zhao
2022-02-10 20:41 ` Johannes Weiner
2022-02-15 9:43 ` Yu Zhao
2022-02-15 21:53 ` Johannes Weiner
2022-02-21 8:14 ` Yu Zhao
2022-02-23 21:18 ` Yu Zhao
2022-02-25 16:34 ` Minchan Kim
2022-03-03 15:29 ` Johannes Weiner
2022-03-03 19:26 ` Yu Zhao
2022-03-03 21:43 ` Johannes Weiner
2022-03-11 10:16 ` Barry Song
2022-03-11 23:45 ` Yu Zhao
2022-03-12 10:37 ` Barry Song
2022-03-12 21:11 ` Yu Zhao
2022-03-13 4:57 ` Barry Song
2022-03-14 11:11 ` Barry Song
2022-03-14 16:45 ` Yu Zhao
2022-03-14 23:38 ` Barry Song
[not found] ` <CAOUHufa9eY44QadfGTzsxa2=hEvqwahXd7Canck5Gt-N6c4UKA@mail.gmail.com>
[not found] ` <CAGsJ_4zvj5rmz7DkW-kJx+jmUT9G8muLJ9De--NZma9ey0Oavw@mail.gmail.com>
2022-03-15 10:29 ` Barry Song
2022-03-16 2:46 ` Yu Zhao
2022-03-16 4:37 ` Barry Song
2022-03-16 5:44 ` Yu Zhao
2022-03-16 6:06 ` Barry Song
2022-03-16 21:37 ` Yu Zhao
2022-02-10 21:37 ` Matthew Wilcox
2022-02-13 21:16 ` Yu Zhao
2022-02-08 8:18 ` [PATCH v7 05/12] mm: multigenerational LRU: minimal implementation Yu Zhao
2022-02-08 8:33 ` Yu Zhao
2022-02-08 16:50 ` Johannes Weiner
2022-02-10 2:53 ` Yu Zhao
2022-02-13 10:04 ` Hillf Danton
2022-02-17 0:13 ` Yu Zhao
2022-02-23 8:27 ` Huang, Ying
2022-02-23 9:36 ` Yu Zhao
2022-02-24 0:59 ` Huang, Ying
2022-02-24 1:34 ` Yu Zhao
2022-02-24 3:31 ` Huang, Ying
2022-02-24 4:09 ` Yu Zhao
2022-02-24 5:27 ` Huang, Ying
2022-02-24 5:35 ` Yu Zhao
2022-02-08 8:18 ` [PATCH v7 06/12] mm: multigenerational LRU: exploit locality in rmap Yu Zhao
2022-02-08 8:40 ` Yu Zhao
2022-02-08 8:18 ` [PATCH v7 07/12] mm: multigenerational LRU: support page table walks Yu Zhao
2022-02-08 8:39 ` Yu Zhao
2022-02-08 8:18 ` [PATCH v7 08/12] mm: multigenerational LRU: optimize multiple memcgs Yu Zhao
2022-02-08 8:18 ` [PATCH v7 09/12] mm: multigenerational LRU: runtime switch Yu Zhao
2022-02-08 8:42 ` Yu Zhao
2022-02-08 8:19 ` [PATCH v7 10/12] mm: multigenerational LRU: thrashing prevention Yu Zhao
2022-02-08 8:43 ` Yu Zhao
2022-02-08 8:19 ` [PATCH v7 11/12] mm: multigenerational LRU: debugfs interface Yu Zhao
2022-02-18 18:56 ` [page-reclaim] " David Rientjes
2022-02-08 8:19 ` [PATCH v7 12/12] mm: multigenerational LRU: documentation Yu Zhao
2022-02-08 8:44 ` Yu Zhao
2022-02-14 10:28 ` Mike Rapoport
2022-02-16 3:22 ` Yu Zhao
2022-02-21 9:01 ` Mike Rapoport
2022-02-22 1:47 ` Yu Zhao
2022-02-23 10:58 ` Mike Rapoport
2022-02-23 21:20 ` Yu Zhao [this message]
2022-02-08 10:11 ` [PATCH v7 00/12] Multigenerational LRU Framework Oleksandr Natalenko
2022-02-08 11:14 ` Michal Hocko
2022-02-08 11:23 ` Oleksandr Natalenko
2022-02-11 20:12 ` Alexey Avramov
2022-02-12 21:01 ` Yu Zhao
2022-03-03 6:06 ` Vaibhav Jain
2022-03-03 6:47 ` Yu Zhao
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