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From: SeongJae Park <sj38.park@gmail.com>
To: Yu Zhao <yuzhao@google.com>
Cc: linux-mm@kvack.org, Andi Kleen <ak@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Benjamin Manes <ben.manes@gmail.com>,
	Dave Chinner <david@fromorbit.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Hillf Danton <hdanton@sina.com>, Jens Axboe <axboe@kernel.dk>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Matthew Wilcox <willy@infradead.org>,
	Mel Gorman <mgorman@suse.de>, Miaohe Lin <linmiaohe@huawei.com>,
	Michael Larabel <michael@michaellarabel.com>,
	Michal Hocko <mhocko@suse.com>,
	Michel Lespinasse <michel@lespinasse.org>,
	Rik van Riel <riel@surriel.com>, Roman Gushchin <guro@fb.com>,
	Rong Chen <rong.a.chen@intel.com>,
	SeongJae Park <sjpark@amazon.de>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Vlastimil Babka <vbabka@suse.cz>, Yang Shi <shy828301@gmail.com>,
	Ying Huang <ying.huang@intel.com>, Zi Yan <ziy@nvidia.com>,
	linux-kernel@vger.kernel.org, lkp@lists.01.org,
	page-reclaim@google.com
Subject: Re: [PATCH v2 00/16] Multigenerational LRU Framework
Date: Tue, 13 Apr 2021 07:51:55 +0000	[thread overview]
Message-ID: <20210413075155.32652-1-sjpark@amazon.de> (raw)
In-Reply-To: <20210413065633.2782273-1-yuzhao@google.com>

From: SeongJae Park <sjpark@amazon.de>

Hello,


Very interesting work, thank you for sharing this :)

On Tue, 13 Apr 2021 00:56:17 -0600 Yu Zhao <yuzhao@google.com> wrote:

> What's new in v2
> ================
> Special thanks to Jens Axboe for reporting a regression in buffered
> I/O and helping test the fix.

Is the discussion open?  If so, could you please give me a link?

> 
> This version includes the support of tiers, which represent levels of
> usage from file descriptors only. Pages accessed N times via file
> descriptors belong to tier order_base_2(N). Each generation contains
> at most MAX_NR_TIERS tiers, and they require additional MAX_NR_TIERS-2
> bits in page->flags. In contrast to moving across generations which
> requires the lru lock, moving across tiers only involves an atomic
> operation on page->flags and therefore has a negligible cost. A
> feedback loop modeled after the well-known PID controller monitors the
> refault rates across all tiers and decides when to activate pages from
> which tiers, on the reclaim path.
> 
> This feedback model has a few advantages over the current feedforward
> model:
> 1) It has a negligible overhead in the buffered I/O access path
>    because activations are done in the reclaim path.
> 2) It takes mapped pages into account and avoids overprotecting pages
>    accessed multiple times via file descriptors.
> 3) More tiers offer better protection to pages accessed more than
>    twice when buffered-I/O-intensive workloads are under memory
>    pressure.
> 
> The fio/io_uring benchmark shows 14% improvement in IOPS when randomly
> accessing Samsung PM981a in the buffered I/O mode.

Improvement under memory pressure, right?  How much pressure?

[...]
> 
> Differential scans via page tables
> ----------------------------------
> Each differential scan discovers all pages that have been referenced
> since the last scan. Specifically, it walks the mm_struct list
> associated with an lruvec to scan page tables of processes that have
> been scheduled since the last scan.

Does this means it scans only virtual address spaces of processes and therefore
pages in the page cache that are not mmap()-ed will not be scanned?

> The cost of each differential scan
> is roughly proportional to the number of referenced pages it
> discovers. Unless address spaces are extremely sparse, page tables
> usually have better memory locality than the rmap. The end result is
> generally a significant reduction in CPU usage, for workloads using a
> large amount of anon memory.

When and how frequently it scans?


Thanks,
SeongJae Park

[...]

  parent reply	other threads:[~2021-04-13  7:52 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-13  6:56 Yu Zhao
2021-04-13  6:56 ` [PATCH v2 01/16] include/linux/memcontrol.h: do not warn in page_memcg_rcu() if !CONFIG_MEMCG Yu Zhao
2021-04-13  6:56 ` [PATCH v2 02/16] include/linux/nodemask.h: define next_memory_node() if !CONFIG_NUMA Yu Zhao
2021-04-13  6:56 ` [PATCH v2 03/16] include/linux/huge_mm.h: define is_huge_zero_pmd() if !CONFIG_TRANSPARENT_HUGEPAGE Yu Zhao
2021-04-13  6:56 ` [PATCH v2 04/16] include/linux/cgroup.h: export cgroup_mutex Yu Zhao
2021-04-13  6:56 ` [PATCH v2 05/16] mm/swap.c: export activate_page() Yu Zhao
2021-04-13  6:56 ` [PATCH v2 06/16] mm, x86: support the access bit on non-leaf PMD entries Yu Zhao
2021-04-13  6:56 ` [PATCH v2 07/16] mm/vmscan.c: refactor shrink_node() Yu Zhao
2021-04-13  6:56 ` [PATCH v2 08/16] mm: multigenerational lru: groundwork Yu Zhao
2021-04-13  6:56 ` [PATCH v2 09/16] mm: multigenerational lru: activation Yu Zhao
2021-04-13  6:56 ` [PATCH v2 10/16] mm: multigenerational lru: mm_struct list Yu Zhao
2021-04-14 14:36   ` Matthew Wilcox
2021-04-13  6:56 ` [PATCH v2 11/16] mm: multigenerational lru: aging Yu Zhao
2021-04-13  6:56 ` [PATCH v2 12/16] mm: multigenerational lru: eviction Yu Zhao
2021-04-13  6:56 ` [PATCH v2 13/16] mm: multigenerational lru: page reclaim Yu Zhao
2021-04-13  6:56 ` [PATCH v2 14/16] mm: multigenerational lru: user interface Yu Zhao
2021-04-13  6:56 ` [PATCH v2 15/16] mm: multigenerational lru: Kconfig Yu Zhao
2021-04-13  6:56 ` [PATCH v2 16/16] mm: multigenerational lru: documentation Yu Zhao
2021-04-13  7:51 ` SeongJae Park [this message]
2021-04-13 16:13   ` [PATCH v2 00/16] Multigenerational LRU Framework Jens Axboe
2021-04-13 16:42     ` SeongJae Park
2021-04-13 23:14     ` Dave Chinner
2021-04-14  2:29       ` Rik van Riel
     [not found]         ` <CAOUHufafMcaG8sOS=1YMy2P_6p0R1FzP16bCwpUau7g1-PybBQ@mail.gmail.com>
2021-04-14  6:15           ` Huang, Ying
2021-04-14  7:58             ` Yu Zhao
2021-04-14  8:27               ` Huang, Ying
2021-04-14 13:51                 ` Rik van Riel
2021-04-14 15:56                   ` Andi Kleen
2021-04-14 15:58                   ` [page-reclaim] " Shakeel Butt
2021-04-14 18:45                   ` Yu Zhao
2021-04-14 15:51           ` Andi Kleen
2021-04-14 15:58             ` Rik van Riel
2021-04-14 19:14               ` Yu Zhao
2021-04-14 19:41                 ` Rik van Riel
2021-04-14 20:08                   ` Yu Zhao
2021-04-14 19:04             ` Yu Zhao
2021-04-15  3:00               ` Andi Kleen
2021-04-15  7:13                 ` Yu Zhao
2021-04-15  8:19                   ` Huang, Ying
2021-04-15  9:57                   ` Michel Lespinasse
2021-04-24  2:33                     ` Yu Zhao
2021-04-24  3:30                       ` Andi Kleen
2021-04-24  4:16                         ` Yu Zhao
2021-04-14  3:40       ` Yu Zhao
2021-04-14  4:50         ` Dave Chinner
2021-04-14  7:16           ` Yu Zhao
2021-04-14 10:00             ` Yu Zhao
2021-04-15  1:36             ` Dave Chinner
2021-04-24 21:21               ` Yu Zhao
2021-04-14 14:43       ` Jens Axboe
2021-04-14 19:42         ` Yu Zhao
2021-04-15  1:21         ` Dave Chinner
2021-04-14 17:43 ` Johannes Weiner
2021-04-27 10:35   ` Yu Zhao
2021-04-29 23:46 ` Konstantin Kharlamov
2021-04-30  6:37   ` Konstantin Kharlamov
2021-04-30 19:31     ` Yu Zhao

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