linux-kernel - Re: [PATCH v8 00/14] Multi-Gen LRU Framework

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Date:   Tue, 8 Mar 2022 17:14:51 -0700
From:   Yu Zhao <yuzhao@...gle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Aneesh Kumar <aneesh.kumar@...ux.ibm.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>,
        Mike Rapoport <rppt@...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 <linux-arm-kernel@...ts.infradead.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Kernel Page Reclaim v2 <page-reclaim@...gle.com>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [PATCH v8 00/14] Multi-Gen LRU Framework

On Tue, Mar 8, 2022 at 5:07 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Tue, Mar 8, 2022 at 3:48 PM Yu Zhao <yuzhao@...gle.com> wrote:
> >
> > The current page reclaim is too expensive in terms of CPU usage and it
> > often makes poor choices about what to evict. This patchset offers an
> > alternative solution that is performant, versatile and
> > straightforward.
>
> So apart from my complaints about asking users config questions that
> simply should not be asked, I really think this just needs to start
> getting merged.
>
> We've seen several numbers on the upsides, and I don't think we'll see
> any of the downsides until we try it. And I don't think there is any
> question that we _shouldn't_ try it, given the numbers posted.
>
> But yeah, I certainly _hope_ that all the benchmarking has been done
> with a unified set of config values, and it's not some kind of bogus
> "cherry-picked config values for this particular machine" kind of
> benchmarking that has been done.
>
> Because that isn't valid benchmarking - comparing some "tuned for this
> paeticular machine or load" setup to a default one is just not worth
> even setting numbers to, and debases the whole value of posting
> results.

All benchmarks were done with the default config values. I'm removing
those config options now.

This sounds self-serving: our data centers want them, so I had to try.