From: Yu Zhao <yuzhao@google.com>
To: Barry Song <21cnbao@gmail.com>
Cc: "Johannes Weiner" <hannes@cmpxchg.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Mel Gorman" <mgorman@suse.de>,
"Michal Hocko" <mhocko@kernel.org>,
"Andi Kleen" <ak@linux.intel.com>,
"Aneesh Kumar" <aneesh.kumar@linux.ibm.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>,
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"Rik van Riel" <riel@surriel.com>,
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LAK <linux-arm-kernel@lists.infradead.org>,
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"Kernel Page Reclaim v2" <page-reclaim@google.com>,
x86 <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 04/12] mm: multigenerational LRU: groundwork
Date: Sat, 12 Mar 2022 14:11:49 -0700 [thread overview]
Message-ID: <CAOUHufbor4L5OfjNFEMcaM5bXnM9VWXw-LK9A04vP65rkcLNMg@mail.gmail.com> (raw)
In-Reply-To: <CAGsJ_4zT7gtGSEoAay=VE6x_YZkNKtLymRL94pBnVgKekPzxaQ@mail.gmail.com>
On Sat, Mar 12, 2022 at 3:37 AM Barry Song <21cnbao@gmail.com> wrote:
>
> On Sat, Mar 12, 2022 at 12:45 PM Yu Zhao <yuzhao@google.com> wrote:
> >
> > On Fri, Mar 11, 2022 at 3:16 AM Barry Song <21cnbao@gmail.com> wrote:
> > >
> > > On Tue, Feb 15, 2022 at 10:43 PM Yu Zhao <yuzhao@google.com> wrote:
> > > >
> > > > On Thu, Feb 10, 2022 at 03:41:57PM -0500, Johannes Weiner wrote:
> > > >
> > > > Thanks for reviewing.
> > > >
> > > > > > +static inline bool lru_gen_is_active(struct lruvec *lruvec, int gen)
> > > > > > +{
> > > > > > + unsigned long max_seq = lruvec->lrugen.max_seq;
> > > > > > +
> > > > > > + VM_BUG_ON(gen >= MAX_NR_GENS);
> > > > > > +
> > > > > > + /* see the comment on MIN_NR_GENS */
> > > > > > + return gen == lru_gen_from_seq(max_seq) || gen == lru_gen_from_seq(max_seq - 1);
> > > > > > +}
> > > > >
> > > > > I'm still reading the series, so correct me if I'm wrong: the "active"
> > > > > set is split into two generations for the sole purpose of the
> > > > > second-chance policy for fresh faults, right?
> > > >
> > > > To be precise, the active/inactive notion on top of generations is
> > > > just for ABI compatibility, e.g., the counters in /proc/vmstat.
> > > > Otherwise, this function wouldn't be needed.
> > >
> > > Hi Yu,
> > > I am still quite confused as i am seeing both active/inactive and lru_gen.
> > > eg:
> > >
> > > root@ubuntu:~# cat /proc/vmstat | grep active
> > > nr_zone_inactive_anon 22797
> > > nr_zone_active_anon 578405
> > > nr_zone_inactive_file 0
> > > nr_zone_active_file 4156
> > > nr_inactive_anon 22800
> > > nr_active_anon 578574
> > > nr_inactive_file 0
> > > nr_active_file 4215
> >
> > Yes, this is expected. We have to maintain the ABI, i.e., the
> > *_active/inactive_* counters.
> >
> > > and:
> > >
> > > root@ubuntu:~# cat /sys//kernel/debug/lru_gen
> > >
> > > ...
> > > memcg 36 /user.slice/user-0.slice/user@0.service
> > > node 0
> > > 20 18820 22 0
> > > 21 7452 0 0
> > > 22 7448 0 0
> > > memcg 33 /user.slice/user-0.slice/user@0.service/app.slice
> > > node 0
> > > 0 2171452 0 0
> > > 1 2171452 0 0
> > > 2 2171452 0 0
> > > 3 2171452 0 0
> > > memcg 37 /user.slice/user-0.slice/session-1.scope
> > > node 0
> > > 42 51804 102127 0
> > > 43 18840 275622 0
> > > 44 16104 216805 1
> > >
> > > Does it mean one page could be in both one of the generations and one
> > > of the active/inactive lists?
> >
> > In terms of the data structure, evictable pages are either on
> > lruvec->lists or lrugen->lists.
> >
> > > Do we have some mapping relationship between active/inactive lists
> > > with generations?
> >
> > For the counters, yes -- pages in max_seq and max_seq-1 are counted as
> > active, and the rest are inactive.
> >
> > > We used to put a faulted file page in inactive, if we access it a
> > > second time, it can be promoted
> > > to active. then in recent years, we have also applied this to anon
> > > pages while kernel adds
> > > workingset protection for anon pages. so basically both anon and file
> > > pages go into the inactive
> > > list for the 1st time, if we access it for the second time, they go to
> > > the active list. if we don't access
> > > it any more, they are likely to be reclaimed as they are inactive.
> > > we do have some special fastpath for code section, executable file
> > > pages are kept on active list
> > > as long as they are accessed.
> >
> > Yes.
> >
> > > so all of the above concerns are actually not that correct?
> >
> > They are valid concerns but I don't know any popular workloads that
> > care about them.
>
> Hi Yu,
> here we can get a workload in Kim's patchset while he added workingset
> protection
> for anon pages:
> https://patchwork.kernel.org/project/linux-mm/cover/1581401993-20041-1-git-send-email-iamjoonsoo.kim@lge.com/
Thanks. I wouldn't call that a workload because it's not a real
application. By popular workloads, I mean applications that the
majority of people actually run on phones, in cloud, etc.
> anon pages used to go to active rather than inactive, but kim's patchset
> moved to use inactive first. then only after the anon page is accessed
> second time, it can move to active.
Yes. To clarify, the A-bit doesn't really mean the first or second
access. It can be many accesses each time it's set.
> "In current implementation, newly created or swap-in anonymous page is
>
> started on the active list. Growing the active list results in rebalancing
> active/inactive list so old pages on the active list are demoted to the
> inactive list. Hence, hot page on the active list isn't protected at all.
>
> Following is an example of this situation.
>
> Assume that 50 hot pages on active list and system can contain total
> 100 pages. Numbers denote the number of pages on active/inactive
> list (active | inactive). (h) stands for hot pages and (uo) stands for
> used-once pages.
>
> 1. 50 hot pages on active list
> 50(h) | 0
>
> 2. workload: 50 newly created (used-once) pages
> 50(uo) | 50(h)
>
> 3. workload: another 50 newly created (used-once) pages
> 50(uo) | 50(uo), swap-out 50(h)
>
> As we can see, hot pages are swapped-out and it would cause swap-in later."
>
> Is MGLRU able to avoid the swap-out of the 50 hot pages?
I think the real question is why the 50 hot pages can be moved to the
inactive list. If they are really hot, the A-bit should protect them.
> since MGLRU
> is putting faulted pages to the youngest generation directly, do we have the
> risk mentioned in Kim's patchset?
There are always risks :) I could imagine a thousand ways to make VM
suffer, but all of them could be irrelevant to how it actually does in
production. So a concrete use case of yours would be much appreciated
for this discussion.
next prev parent reply other threads:[~2022-03-12 21:12 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 [this message]
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
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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