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From:   Barry Song <21cnbao@gmail.com>
Date:   Sat, 19 Mar 2022 16:01:13 +1300
Message-ID: <CAGsJ_4xfL7h6M92WGusxbTxQzHOJDj4X4AuC=0HgrEyAYJaJFg@mail.gmail.com>
Subject: Re: [PATCH v9 06/14] mm: multi-gen LRU: minimal implementation
To:     Yu Zhao <yuzhao@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andi Kleen <ak@linux.intel.com>,
        Aneesh Kumar <aneesh.kumar@linux.ibm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Hillf Danton <hdanton@sina.com>, Jens Axboe <axboe@kernel.dk>,
        Jesse Barnes <jsbarnes@google.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Matthew Wilcox <willy@infradead.org>,
        Mel Gorman <mgorman@suse.de>,
        Michael Larabel <Michael@michaellarabel.com>,
        Michal Hocko <mhocko@kernel.org>,
        Mike Rapoport <rppt@kernel.org>,
        Rik van Riel <riel@surriel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Will Deacon <will@kernel.org>,
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        Kernel Page Reclaim v2 <page-reclaim@google.com>,
        x86 <x86@kernel.org>, Brian Geffon <bgeffon@google.com>,
        Jan Alexander Steffens <heftig@archlinux.org>,
        Oleksandr Natalenko <oleksandr@natalenko.name>,
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        =?UTF-8?Q?Holger_Hoffst=C3=A4tte?= <holger@applied-asynchrony.com>,
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Precedence: bulk

> +static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, bool reclaiming)
> +{
> +       unsigned long old_flags, new_flags;
> +       int type = folio_is_file_lru(folio);
> +       struct lru_gen_struct *lrugen = &lruvec->lrugen;
> +       int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
> +
> +       do {
> +               new_flags = old_flags = READ_ONCE(folio->flags);
> +               VM_BUG_ON_FOLIO(!(new_flags & LRU_GEN_MASK), folio);
> +
> +               new_gen = ((new_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
> +               new_gen = (old_gen + 1) % MAX_NR_GENS;

new_gen is assigned twice, i assume you mean
               old_gen = ((new_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
               new_gen = (old_gen + 1) % MAX_NR_GENS;

or do you always mean new_gen =  lru_gen_from_seq(min_seq) + 1?

> +
> +               new_flags &= ~LRU_GEN_MASK;
> +               new_flags |= (new_gen + 1UL) << LRU_GEN_PGOFF;
> +               new_flags &= ~(LRU_REFS_MASK | LRU_REFS_FLAGS);
> +               /* for folio_end_writeback() */
> +               if (reclaiming)
> +                       new_flags |= BIT(PG_reclaim);
> +       } while (cmpxchg(&folio->flags, old_flags, new_flags) != old_flags);
> +
> +       lru_gen_update_size(lruvec, folio, old_gen, new_gen);
> +
> +       return new_gen;
> +}
> +

Thanks
Barry