linux-kernel - Re: [PATCH] ksm: Expose configuration via sysctl

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Date:	Tue, 25 Feb 2014 18:19:40 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Alexander Graf <agraf@...e.de>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Rik van Riel <riel@...hat.com>,
	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Hugh Dickins <hughd@...gle.com>,
	Izik Eidus <izik.eidus@...ellosystems.com>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH] ksm: Expose configuration via sysctl

On Tue, Feb 25, 2014 at 12:15:28PM -0500, Johannes Weiner wrote:
> On Tue, Feb 25, 2014 at 12:28:04AM +0100, Alexander Graf wrote:
> > Configuration of tunables and Linux virtual memory settings has traditionally
> > happened via sysctl. Thanks to that there are well established ways to make
> > sysctl configuration bits persistent (sysctl.conf).
> > 
> > KSM introduced a sysfs based configuration path which is not covered by user
> > space persistent configuration frameworks.
> > 
> > In order to make life easy for sysadmins, this patch adds all access to all
> > KSM tunables via sysctl as well. That way sysctl.conf works for KSM as well,
> > giving us a streamlined way to make KSM configuration persistent.
> > 
> > Reported-by: Sasche Peilicke <speilicke@...e.com>
> > Signed-off-by: Alexander Graf <agraf@...e.de>
> > ---
> >  kernel/sysctl.c |   10 +++++++
> >  mm/ksm.c        |   78 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 88 insertions(+), 0 deletions(-)
> > 
> > diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> > index 332cefc..2169a00 100644
> > --- a/kernel/sysctl.c
> > +++ b/kernel/sysctl.c
> > @@ -217,6 +217,9 @@ extern struct ctl_table random_table[];
> >  #ifdef CONFIG_EPOLL
> >  extern struct ctl_table epoll_table[];
> >  #endif
> > +#ifdef CONFIG_KSM
> > +extern struct ctl_table ksm_table[];
> > +#endif
> >  
> >  #ifdef HAVE_ARCH_PICK_MMAP_LAYOUT
> >  int sysctl_legacy_va_layout;
> > @@ -1279,6 +1282,13 @@ static struct ctl_table vm_table[] = {
> >  	},
> >  
> >  #endif /* CONFIG_COMPACTION */
> > +#ifdef CONFIG_KSM
> > +	{
> > +		.procname	= "ksm",
> > +		.mode		= 0555,
> > +		.child		= ksm_table,
> > +	},
> > +#endif
> 
> ksm can be a module, so this won't work.
> 
> Can we make those controls proper module parameters instead?

You can do dynamic sysctl registration and removal. Its its own little
filesystem of sorts.
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