linux-kernel - Re: [PATCH v9 05/14] mm: multi-gen LRU: groundwork

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Message-ID: <CAOUHufY8_f353GivFy=_2g=DHmQJcBHNzbabhyGhMnoBbzL8yQ@mail.gmail.com>
Date:   Mon, 14 Mar 2022 18:50:08 -0600
From:   Yu Zhao <yuzhao@...gle.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     kernel@...ts.fedoraproject.org, kernel-team@...ts.ubuntu.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...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>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        linux-kernel <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>,
        Brian Geffon <bgeffon@...gle.com>,
        Jan Alexander Steffens <heftig@...hlinux.org>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
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        Holger Hoffstätte <holger@...lied-asynchrony.com>,
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        Shuang Zhai <szhai2@...rochester.edu>,
        Sofia Trinh <sofia.trinh@....works>,
        Vaibhav Jain <vaibhav@...ux.ibm.com>
Subject: Re: [PATCH v9 05/14] mm: multi-gen LRU: groundwork

On Mon, Mar 14, 2022 at 6:34 PM Huang, Ying <ying.huang@...el.com> wrote:
>
> Yu Zhao <yuzhao@...gle.com> writes:
>
> > On Mon, Mar 14, 2022 at 2:09 AM Huang, Ying <ying.huang@...el.com> wrote:
> >>
> >> Hi, Yu,
> >>
> >> Yu Zhao <yuzhao@...gle.com> writes:
> >> > diff --git a/mm/Kconfig b/mm/Kconfig
> >> > index 3326ee3903f3..747ab1690bcf 100644
> >> > --- a/mm/Kconfig
> >> > +++ b/mm/Kconfig
> >> > @@ -892,6 +892,16 @@ config ANON_VMA_NAME
> >> >         area from being merged with adjacent virtual memory areas due to the
> >> >         difference in their name.
> >> >
> >> > +# the multi-gen LRU {
> >> > +config LRU_GEN
> >> > +     bool "Multi-Gen LRU"
> >> > +     depends on MMU
> >> > +     # the following options can use up the spare bits in page flags
> >> > +     depends on !MAXSMP && (64BIT || !SPARSEMEM || SPARSEMEM_VMEMMAP)
> >>
> >> LRU_GEN depends on !MAXSMP.  So, What is the maximum NR_CPUS supported
> >> by LRU_GEN?
> >
> > LRU_GEN doesn't really care about NR_CPUS. IOW, it doesn't impose a
> > max number. The dependency is with NODES_SHIFT selected by MAXSMP:
> >     default "10" if MAXSMP
> > This combined with LAST_CPUPID_SHIFT can exhaust the spare bits in page flags.
>
> From the following code snippets from page-flags-layout.h,
> LAST_CPUPID_SHIFT is related to NR_CPUS instead of NODES_SHIFT.

It is. But LAST_CPUPID_NOT_IN_PAGE_FLAGS should always work but
NODE_NOT_IN_PAGE_FLAGS doesn't.