linux-kernel - Re: [PATCH 07/10] mm/vmscan: add helper for querying ability to age anonymous pages

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Message-ID: <CAAPL-u-OgmT+R=txfO_rFaYLKC0UZ5xEmFOY3spVHEmk_r4iSQ@mail.gmail.com>
Date:   Wed, 7 Apr 2021 11:40:13 -0700
From:   Wei Xu <weixugc@...gle.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        shy828301@...il.com, Greg Thelen <gthelen@...gle.com>,
        David Rientjes <rientjes@...gle.com>, ying.huang@...el.com,
        Dan Williams <dan.j.williams@...el.com>, david@...hat.com,
        osalvador@...e.de
Subject: Re: [PATCH 07/10] mm/vmscan: add helper for querying ability to age
 anonymous pages

> +/*
> + * Anonymous LRU management is a waste if there is
> + * ultimately no way to reclaim the memory.
> + */
> +bool anon_should_be_aged(struct lruvec *lruvec)
> +{
> +       struct pglist_data *pgdat = lruvec_pgdat(lruvec);
> +
> +       /* Aging the anon LRU is valuable if swap is present: */
> +       if (total_swap_pages > 0)
> +               return true;
> +
> +       /* Also valuable if anon pages can be demoted: */
> +       if (next_demotion_node(pgdat->node_id) >= 0)
> +               return true;
> +
> +       /* No way to reclaim anon pages.  Should not age anon LRUs: */
> +       return false;
> +}

anon_should_be_aged() doesn't really need "lruvec".  It essentially
answers whether the pages of the given node can be swapped or demoted.
So it would be clearer and less confusing if anon_should_be_aged()
takes "pgdat" instead of "lruvec" as the argument.  The call to
mem_cgroup_lruvec(NULL, pgdat) in age_active_anon() can then be removed
as well.