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

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Date:   Fri, 23 Apr 2021 20:30:38 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Michel Lespinasse <michel@...pinasse.org>,
        Rik van Riel <riel@...riel.com>,
        Ying Huang <ying.huang@...el.com>,
        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>, 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>, 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

> Now the question is how we build the bloom filter. A simple answer is
> to let the rmap do the legwork, i.e., when it encounters dense
> regions, add them to the filter. Of course this means we'll have to
> use the rmap more than we do now, which is not ideal for some
> workloads but necessary to avoid worst case scenarios.

How would you maintain the bloom filter over time? Assume a process
that always creates new mappings and unmaps old mappings. How 
do the stale old mappings get removed and avoid polluting it over time?

Or are you thinking of one of the fancier bloom filter variants
that support deletion? As I understand they're significantly less
space efficient and more complicated.

-Andi