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

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Date:	Wed, 26 Feb 2014 18:32:08 +0100
From:	Alexander Graf <agraf@...e.de>
To:	Sven-Haegar Koch <haegar@...net.de>
CC:	Dave Hansen <dave.hansen@...el.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.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

Sven-Haegar Koch wrote:
> On Tue, 25 Feb 2014, Dave Hansen wrote:
>
>   
>> On 02/25/2014 03:09 PM, Alexander Graf wrote:
>>     
>>>> Couldn't we also (maybe in parallel) just teach the sysctl userspace
>>>> about sysfs?  This way we don't have to do parallel sysctls and sysfs
>>>> for *EVERYTHING* in the kernel:
>>>>
>>>>    sysfs.kernel.mm.transparent_hugepage.enabled=enabled
>>>>         
>>> It's pretty hard to filter this. We definitely do not want to expose all of sysfs through /proc/sys. But how do we know which files are actual configuration and which ones are dynamic system introspection data?
>>>
>>> We could add a filter, but then we can just as well stick with the manual approach I followed here :).
>>>       
>> Maybe not stick it under /proc/sys, but teach sysctl(8) about them.  I
>> guess at the moment, sysctl says that it's tied to /proc/sys:
>>
>>     
>>> DESCRIPTION
>>>        sysctl  is  used to modify kernel parameters at runtime.  The parameters available are those listed under /proc/sys/.  Procfs is required
>>>        for sysctl support in Linux.  You can use sysctl to both read and write sysctl data.
>>>       
>> But surely that's not set in stone just because the manpage says so. :)
>>     
>
> What I still don't get is why you need this?
>
> My distribution (Debian) has a sysfsutils package which provides a 
> /etc/sysfs.conf / /etc/sysfs.d/foo exactly like /etc/sysctl.conf.
>
> Don't other distributions have something like this?
>   

Maybe that's the right answer to the problem, but I still don't
understand why these properties were put into sysfs in the first place.
We're not configuring a dynamic device here, are we?

Also if we do want something like a sysfs.conf and sysfs.d, that should
probably be something that gets properly coordinated between
distributions so that users don't get completely confused. Today
openSUSE does not have a sysfs.conf/.d provided by the sysfsutils
package. Maybe it's something homegrown?


Alex

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