linux-kernel - Re: [PATCH v6 0/9] Multigenerational LRU Framework

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Message-ID: <20220111192451.1a853019@mail.inbox.lv>
Date:   Tue, 11 Jan 2022 19:24:51 +0900
From:   Alexey Avramov <hakavlad@...ox.lv>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Hillf Danton <hdanton@...a.com>, Jens Axboe <axboe@...nel.dk>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Michael Larabel <Michael@...haellarabel.com>,
        Michal Hocko <mhocko@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Will Deacon <will@...nel.org>,
        Ying Huang <ying.huang@...el.com>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        page-reclaim@...gle.com, x86@...nel.org, hakavlad@...il.com
Subject: Re: [PATCH v6 0/9] Multigenerational LRU Framework

In some of my benchmarks MGLRU really gave unrivaled performance.
I assume the adoption of MGLRU into the kernel would save billions of
dollars and greatly reduce carbon dioxide emissions.

However, there are also cases where MGLRU loses.
There are cases where MGLRU does not achieve the performance that the
classic LRU gives (at least I got such results when testing MGLRU before[1],
but I did not report them here).

As a Linux user, I would like to see both variants of LRU in the kernel, so
that it is possible to switch to the suitable variant when needed: none of
the LRU variants allowed me to squeeze the maximum for all cases.

I hope to test MGLRU v6 later and show you some of its weaknesses and
anomalies with specific logs and benchmarks. 

[1] I didn't have enough time and energy to decipher the results at that time:
    https://github.com/hakavlad/cache-tests/tree/main/mg-LRU-v3_vs_classic-LRU
    (but you can try to guess what it all means)