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SubjectRe: [patch] drop_caches: add some documentation and info message
On Fri, 7 Feb 2014 16:26:01 -0500 Johannes Weiner <hannes@cmpxchg.org> wrote:

> On Fri, Feb 07, 2014 at 12:31:29PM -0800, Andrew Morton wrote:
> > On Fri, 7 Feb 2014 13:13:32 -0500 Johannes Weiner <hannes@cmpxchg.org> wrote:
> >
> > > @@ -63,6 +64,9 @@ int drop_caches_sysctl_handler(ctl_table *table, int write,
> > > iterate_supers(drop_pagecache_sb, NULL);
> > > if (sysctl_drop_caches & 2)
> > > drop_slab();
> > > + printk_ratelimited(KERN_INFO "%s (%d): dropped kernel caches: %d\n",
> > > + current->comm, task_pid_nr(current),
> > > + sysctl_drop_caches);
> > > }
> > > return 0;
> > > }
> >
> > My concern with this is that there may be people whose
> > other-party-provided software uses drop_caches. Their machines will
> > now sit there emitting log messages and there's nothing they can do
> > about it, apart from whining at their vendors.
>
> Ironically, we have a customer that is complaining that we currently
> do not log these events, and they want to know who in their stack is
> being idiotic.

Right. But if we release a kernel which goes blah on every write to
drop_caches, that customer has logs full of blahs which they are
now totally uninterested in.

> > We could do something like this?
>
> They can already change the log level.

Suppressing unrelated things...

> The below will suppress
> valuable debugging information in a way that still results in
> inconspicuous looking syslog excerpts, which somewhat undermines the
> original motivation for this change.

Yes, somewhat. It is a compromise. You can see my concern here?




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