linux-kernel - Re: [patch] drop_caches: add some documentation and info message

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Message-Id: <20140211134459.551dd07d697a888e29f1c7b1@linux-foundation.org>
Date:	Tue, 11 Feb 2014 13:44:59 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Rik van Riel <riel@...hat.com>, Dave Hansen <dave@...1.net>,
	Michal Hocko <mhocko@...e.cz>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [patch] drop_caches: add some documentation and info message

On Mon, 10 Feb 2014 16:54:16 -0500 Johannes Weiner <hannes@...xchg.org> wrote:

> How about this: we allow disabling the log message, but print the line
> of the disabling call so it's clear who dunnit.  To make sure valuable
> info is not missing in bug reports, add counters for the two events in
> /proc/vmstat.
> 
> Does that sound acceptable?

Yes, I really don't know what's the right thing to do here or where the
best tradeoff point is situated.  Let's start off this way and see what
happens I guess.

> --- a/fs/drop_caches.c
> +++ b/fs/drop_caches.c
> @@ -59,10 +59,22 @@ int drop_caches_sysctl_handler(ctl_table *table, int write,
>  	if (ret)
>  		return ret;
>  	if (write) {
> -		if (sysctl_drop_caches & 1)
> +		static int stfu;

That identifier wasn't serious, but I kinda like it.

> +
> +		if (sysctl_drop_caches & 1) {
>  			iterate_supers(drop_pagecache_sb, NULL);
> -		if (sysctl_drop_caches & 2)
> +			count_vm_event(DROP_PAGECACHE);
> +		}
> +		if (sysctl_drop_caches & 2) {
>  			drop_slab();
> +			count_vm_event(DROP_SLAB);
> +		}
> +		if (!stfu) {
> +			pr_info("%s (%d): drop_caches: %d\n",
> +				current->comm, task_pid_nr(current),
> +				sysctl_drop_caches);
> +		}
> +		stfu |= sysctl_drop_caches & 4;
>  	}
>  	return 0;
>  }

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