linux-kernel - Re: [PATCH v2 00/16] Multigenerational LRU Framework

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Message-ID: <e0ad1b48a1ad0b6d3a1e79129f397ddb6c32fe35.camel@surriel.com>
Date:   Wed, 14 Apr 2021 11:58:53 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Andi Kleen <ak@...ux.intel.com>, Yu Zhao <yuzhao@...gle.com>
Cc:     Dave Chinner <david@...morbit.com>, Jens Axboe <axboe@...nel.dk>,
        SeongJae Park <sj38.park@...il.com>,
        Linux-MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Benjamin Manes <ben.manes@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Hillf Danton <hdanton@...a.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Michael Larabel <michael@...haellarabel.com>,
        Michal Hocko <mhocko@...e.com>,
        Michel Lespinasse <michel@...pinasse.org>,
        Roman Gushchin <guro@...com>,
        Rong Chen <rong.a.chen@...el.com>,
        SeongJae Park <sjpark@...zon.de>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Yang Shi <shy828301@...il.com>,
        Ying Huang <ying.huang@...el.com>, Zi Yan <ziy@...dia.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        Kernel Page Reclaim v2 <page-reclaim@...gle.com>
Subject: Re: [PATCH v2 00/16] Multigenerational LRU Framework

On Wed, 2021-04-14 at 08:51 -0700, Andi Kleen wrote:
> >    2) It will not scan PTE tables under non-leaf PMD entries that
> > do not
> >       have the accessed bit set, when
> >       CONFIG_HAVE_ARCH_PARENT_PMD_YOUNG=y.
> 
> This assumes  that workloads have reasonable locality. Could there
> be a worst case where only one or two pages in each PTE are used,
> so this PTE skipping trick doesn't work?

Databases with large shared memory segments shared between
many processes come to mind as a real-world example of a
worst case scenario.

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