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SubjectRe: [PATCH] Make /proc/sys/vm/drop_caches write only
On Thu, 13 Nov 2008 17:54:11 +0530
Nikanth Karthikesan <knikanth@suse.de> wrote:

> /proc/sys/vm/drop_caches is used only to trigger dropping caches. It does not
> disable the cache. The ability to read the value written to this file long
> back gives wrong impression.
>
> Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>
>
> ---
>
> diff --git a/fs/drop_caches.c b/fs/drop_caches.c
> index 3e5637f..9892e1b 100644
> --- a/fs/drop_caches.c
> +++ b/fs/drop_caches.c
> @@ -66,11 +66,9 @@ int drop_caches_sysctl_handler(ctl_table *table, int write,
> struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
> {
> proc_dointvec_minmax(table, write, file, buffer, length, ppos);
> - if (write) {
> - if (sysctl_drop_caches & 1)
> - drop_pagecache();
> - if (sysctl_drop_caches & 2)
> - drop_slab();
> - }
> + if (sysctl_drop_caches & 1)
> + drop_pagecache();
> + if (sysctl_drop_caches & 2)
> + drop_slab();
> return 0;
> }
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 9d048fa..dff3c13 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1015,7 +1015,7 @@ 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,
> .strategy = &sysctl_intvec,
> },

True. But it's a backward-incompatible change, and there's a (small)
chance that someone's tools will break if we do this.

We have to get these things right first time :(


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