linux-kernel - Re: [PATCH v9 10/14] mm: multi-gen LRU: kill switch

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Message-ID: <CAOUHufbP7kHquWiD3VsmD=veNFF2v_E9HWqdYSMbS1nPJic0Fg@mail.gmail.com>
Date:   Tue, 22 Mar 2022 02:20:20 -0600
From:   Yu Zhao <yuzhao@...gle.com>
To:     Barry Song <21cnbao@...il.com>
Cc:     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>,
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        Jonathan Corbet <corbet@....net>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Michael Larabel <Michael@...haellarabel.com>,
        Michal Hocko <mhocko@...nel.org>,
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        Vlastimil Babka <vbabka@...e.cz>,
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        LAK <linux-arm-kernel@...ts.infradead.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
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        Shuang Zhai <szhai2@...rochester.edu>,
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        Vaibhav Jain <vaibhav@...ux.ibm.com>
Subject: Re: [PATCH v9 10/14] mm: multi-gen LRU: kill switch

On Tue, Mar 22, 2022 at 1:47 AM Barry Song <21cnbao@...il.com> wrote:
>
...
> > +static bool drain_evictable(struct lruvec *lruvec)
> > +{
> > +       int gen, type, zone;
> > +       int remaining = MAX_LRU_BATCH;
> > +
> > +       for_each_gen_type_zone(gen, type, zone) {
> > +               struct list_head *head = &lruvec->lrugen.lists[gen][type][zone];
> > +
> > +               while (!list_empty(head)) {
> > +                       bool success;
> > +                       struct folio *folio = lru_to_folio(head);
> > +
> > +                       VM_BUG_ON_FOLIO(folio_test_unevictable(folio), folio);
> > +                       VM_BUG_ON_FOLIO(folio_test_active(folio), folio);
> > +                       VM_BUG_ON_FOLIO(folio_is_file_lru(folio) != type, folio);
> > +                       VM_BUG_ON_FOLIO(folio_zonenum(folio) != zone, folio);
> > +
> > +                       success = lru_gen_del_folio(lruvec, folio, false);
> > +                       VM_BUG_ON(!success);
> > +                       lruvec_add_folio(lruvec, folio);
>
> for example, max_seq=4(GEN=0) and max_seq-1=3, then we are supposed to put
> max_seq in the head of active list. but your code seems to be putting max_seq-1
> after putting max_seq, then max_seq is more likely to be evicted
> afterwards as it
> is in the tail of the active list.

This is correct.

> anyway, it might not be so important. I can't imagine we will
> frequently switch mglru
> with lru dynamically. will we?

I certainly hope not :)