linux-kernel - Re: [PATCH] mm/list_lru: optimize condition of exiting the loop

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Message-ID: <ae359cb8-5bf9-c2e5-ddd0-812df81de0fb@suse.cz>
Date:   Tue, 27 Oct 2020 19:45:53 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Hui Su <sh_def@....com>, akpm@...ux-foundation.org,
        gustavo@...eddedor.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH] mm/list_lru: optimize condition of exiting the loop

On 10/27/20 6:04 PM, Hui Su wrote:
> 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@....com>

OK. Why not this too?

--- 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];


> ---
>   include/linux/list_lru.h | 2 +-
>   mm/list_lru.c            | 2 +-
>   2 files changed, 2 insertions(+), 2 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..39b8d467159d 100644
> --- a/mm/list_lru.c
> +++ b/mm/list_lru.c
> @@ -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;
>   		}
>   	}
>