linux-kernel - Re: [PATCH] rcu/kvfree: Make drain_page_cache() call return directly if cache is disabled

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Message-ID: <ZD6HdrXAueycm/bX@pc636>
Date:   Tue, 18 Apr 2023 14:05:10 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Zqiang <qiang1.zhang@...el.com>
Cc:     urezki@...il.com, paulmck@...nel.org, frederic@...nel.org,
        joel@...lfernandes.org, qiang.zhang1211@...il.com,
        rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu/kvfree: Make drain_page_cache() call return directly
 if cache is disabled

On Tue, Apr 18, 2023 at 03:02:59PM +0800, Zqiang wrote:
> If the rcu_min_cached_objs is set to zero at boot params, the
> krcp->page_cache_work will not be triggered to fill page cache,
> and the put_cached_bnode() also does not fill page cache, this
> also means the krcp->bkvcache is always empty, so not need to
> acquire unnecessary krcp->lock to get page from krcp->bkvcache,
> this commit therefore make drain_page_cache() return directly if
> the rcu_min_cached_objs is zero.
> 
> Signed-off-by: Zqiang <qiang1.zhang@...el.com>
> ---
>  kernel/rcu/tree.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index c8ba2be026fa..ce995fc1c644 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2924,6 +2924,9 @@ drain_page_cache(struct kfree_rcu_cpu *krcp)
>  	struct llist_node *page_list, *pos, *n;
>  	int freed = 0;
>  
> +	if (rcu_min_cached_objs)
> +		return 0;
> +
>
Should we check for zero?

--
Uladzislau Rezki