linux-kernel - Re: [PATCH] kernel: sysctl: make drop

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Message-ID: <e8b6cbe6-2a38-1c72-2f22-fe3b6819e75c@suse.cz>
Date:   Mon, 4 Nov 2019 14:25:54 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH] kernel: sysctl: make drop_caches write-only

On 10/31/19 11:16 PM, Johannes Weiner wrote:
> Currently, the drop_caches proc file and sysctl read back the last
> value written, suggesting this is somehow a stateful setting instead
> of a one-time command. Make it write-only, like e.g. compact_memory.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

Generic tools such as "sysctl -a" will be fine as they already are fine
with compact_memory being 0200, and if somebody has a specific script,
they are maybe already making wrong decisions, so at least hopefully
they will learn and adjust.

> ---
>  kernel/sysctl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 31ece1120aa4..50373984a5e2 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1474,7 +1474,7 @@ static struct ctl_table vm_table[] = {
>  		.procname	= "drop_caches",
>  		.data		= &sysctl_drop_caches,
>  		.maxlen		= sizeof(int),
> -		.mode		= 0644,
> +		.mode		= 0200,
>  		.proc_handler	= drop_caches_sysctl_handler,
>  		.extra1		= SYSCTL_ONE,
>  		.extra2		= &four,
>