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From:   Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Date:   Mon, 2 Nov 2020 14:44:39 +0100
Message-ID: <CAM9Jb+gsuN_0Wo8XKP8jnLi+gCT-EX5UJBraDPd5zUn9NeOqsw@mail.gmail.com>
Subject: Re: [PATCH v2] mm/list_lru: optimize condition of exiting the loop
To:     Hui Su <sh_def@163.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, gustavo@embeddedor.com,
        Muchun Song <songmuchun@bytedance.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>
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> In list_lru_walk(), nr_to_walk type is 'unsigned long',
> so nr_to_walk won't be '< 0'.
>
> In list_lru_walk_node(), nr_to_walk type is 'unsigned long',
> so *nr_to_walk won't be '< 0' too.
>
> We can use '!nr_to_walk' instead of 'nr_to_walk <= 0', which
> is more precise.
>
> Signed-off-by: Hui Su <sh_def@163.com>
> ---
>  include/linux/list_lru.h | 2 +-
>  mm/list_lru.c            | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
> index 9dcaa3e582c9..b7bc4a2636b9 100644
> --- a/include/linux/list_lru.h
> +++ b/include/linux/list_lru.h
> @@ -214,7 +214,7 @@ list_lru_walk(struct list_lru *lru, list_lru_walk_cb isolate,
>         for_each_node_state(nid, N_NORMAL_MEMORY) {
>                 isolated += list_lru_walk_node(lru, nid, isolate,
>                                                cb_arg, &nr_to_walk);
> -               if (nr_to_walk <= 0)
> +               if (!nr_to_walk)
>                         break;
>         }
>         return isolated;
> diff --git a/mm/list_lru.c b/mm/list_lru.c
> index 5aa6e44bc2ae..35be4de9fd77 100644
> --- a/mm/list_lru.c
> +++ b/mm/list_lru.c
> @@ -294,7 +294,7 @@ unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
>
>         isolated += list_lru_walk_one(lru, nid, NULL, isolate, cb_arg,
>                                       nr_to_walk);
> -       if (*nr_to_walk > 0 && list_lru_memcg_aware(lru)) {
> +       if (*nr_to_walk && list_lru_memcg_aware(lru)) {
>                 for_each_memcg_cache_index(memcg_idx) {
>                         struct list_lru_node *nlru = &lru->node[nid];
>
> @@ -304,7 +304,7 @@ unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
>                                                         nr_to_walk);
>                         spin_unlock(&nlru->lock);
>
> -                       if (*nr_to_walk <= 0)
> +                       if (!*nr_to_walk)
>                                 break;
>                 }
>         }

Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>