From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-bk0-f52.google.com (mail-bk0-f52.google.com [209.85.214.52]) by kanga.kvack.org (Postfix) with ESMTP id 30A926B0031 for ; Fri, 22 Nov 2013 02:39:10 -0500 (EST) Received: by mail-bk0-f52.google.com with SMTP id u14so654705bkz.25 for ; Thu, 21 Nov 2013 23:39:09 -0800 (PST) Received: from mail-la0-x234.google.com (mail-la0-x234.google.com [2a00:1450:4010:c03::234]) by mx.google.com with ESMTPS id ch7si5575483bkc.31.2013.11.21.23.39.09 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 21 Nov 2013 23:39:09 -0800 (PST) Received: by mail-la0-f52.google.com with SMTP id ev20so619282lab.39 for ; Thu, 21 Nov 2013 23:39:08 -0800 (PST) Date: Fri, 22 Nov 2013 08:38:54 +0100 From: Vladimir Murzin Subject: Re: [PATCH] mm/zswap: change params from hidden to ro Message-ID: <20131122073851.GB1853@hp530> References: <1384965522-5788-1-git-send-email-ddstreet@ieee.org> <20131120173347.GA2369@hp530> MIME-Version: 1.0 Content-Type: text/plain; charset=koi8-r Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Dan Streetman Cc: linux-mm@kvack.org, Seth Jennings , linux-kernel , Bob Liu , Minchan Kim , Weijie Yang On Wed, Nov 20, 2013 at 12:52:47PM -0500, Dan Streetman wrote: > On Wed, Nov 20, 2013 at 12:33 PM, Vladimir Murzin wrote: > > Hi Dan! > > > > On Wed, Nov 20, 2013 at 11:38:42AM -0500, Dan Streetman wrote: > >> The "compressor" and "enabled" params are currently hidden, > >> this changes them to read-only, so userspace can tell if > >> zswap is enabled or not and see what compressor is in use. > > > > Could you elaborate more why this pice of information is necessary for > > userspace? > > For anyone interested in zswap, it's handy to be able to tell if it's > enabled or not ;-) Technically people can check to see if the zswap > debug files are in /sys/kernel/debug/zswap, but I think the actual > "enabled" param is more obvious. And the compressor param is really > the only way anyone from userspace can see what compressor's being > used; that's helpful to know for anyone that might want to be using a > non-default compressor. So, it is needed for user not userspace? I tend to think that users are smart enough to check cmdline for that. AFAICS module_param exist here to provide simplest ability to handle the setting via cmdline. zsawap is not able to be loaded as a module for now. If it could, than there was reason to check which params were used while module loading and guess how they affected zswap state. > > And of course, eventually we'll want to make the params writable, so > the compressor can be changed dynamically, and zswap can be enabled or > disabled dynamically (or at least enabled after boot). module_params is not the best place to handle this, because they do not provide any hooks for handling write unless I missed something. However, making zswap state dynamically adjustable require not only setting the numbers, but handling the correctness switching from one state to another. Vladimir -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org