From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932325Ab1IAWIK (ORCPT ); Thu, 1 Sep 2011 18:08:10 -0400 Received: from smtp-out.google.com ([216.239.44.51]:7493 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932200Ab1IAWII (ORCPT ); Thu, 1 Sep 2011 18:08:08 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=dkim-signature:date:from:x-x-sender:to:cc:subject: in-reply-to:message-id:references:user-agent:mime-version:content-type:x-system-of-record; b=ECcUtY/pn1nmhHsTsyVPZ0Sv1gRGyOYrmojIf51NT3RYxDNQmO43G6bZ2In6y7Go7 VpFJWipoeG/UrZrcykSNg== Date: Thu, 1 Sep 2011 15:08:00 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Andrew Morton cc: Rik van Riel , Randy Dunlap , Satoru Moriya , linux-kernel@vger.kernel.org, linux-mm@kvack.org, lwoodman@redhat.com, Seiji Aguchi , hughd@google.com, hannes@cmpxchg.org Subject: Re: [PATCH -v2 -mm] add extra free kbytes tunable In-Reply-To: <20110901145819.4031ef7c.akpm@linux-foundation.org> Message-ID: References: <20110901105208.3849a8ff@annuminas.surriel.com> <20110901100650.6d884589.rdunlap@xenotime.net> <20110901152650.7a63cb8b@annuminas.surriel.com> <20110901145819.4031ef7c.akpm@linux-foundation.org> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 1 Sep 2011, Andrew Morton wrote: > > Add a userspace visible knob > > argh. Fear and hostility at new knobs which need to be maintained for > ever, even if the underlying implementation changes. > Do we really need to maintain tunables that lose their purpose either because the implementation changes or is patched to fix the issue that the tunable was intended to address without requiring it? Are there really userspace tools written to not be able to handle -ENOENT when one of these gets removed? > > It may also be useful to reduce the memory use of virtual > > machines (temporarily?), in a way that does not cause memory > > fragmentation like ballooning does. > > Maybe. You need to alter the setting, then somehow persuade all the > targeted kswapd's to start running, then somehow determine that they've > done their thing, then unalter the /proc setting. Not the best API > we've ever designed ;) > And, unfortunately, this could have negative effects if using cpusets and/or mempolicies since this is global across all zones such that jobs that do not require such "extra" memory would be unfairly penalized with work incurred by additional reclaim they don't need. And if the job is constrained to a memory cgroup, there's no guarantee it will reclaim back to these altered watermarks. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with ESMTP id A58C36B016A for ; Thu, 1 Sep 2011 18:08:17 -0400 (EDT) Received: from hpaq11.eem.corp.google.com (hpaq11.eem.corp.google.com [172.25.149.11]) by smtp-out.google.com with ESMTP id p81M86Ci028296 for ; Thu, 1 Sep 2011 15:08:07 -0700 Received: from gwb1 (gwb1.prod.google.com [10.200.2.1]) by hpaq11.eem.corp.google.com with ESMTP id p81M5qGb032397 (version=TLSv1/SSLv3 cipher=RC4-SHA bits=128 verify=NOT) for ; Thu, 1 Sep 2011 15:08:05 -0700 Received: by gwb1 with SMTP id 1so1419467gwb.36 for ; Thu, 01 Sep 2011 15:08:02 -0700 (PDT) Date: Thu, 1 Sep 2011 15:08:00 -0700 (PDT) From: David Rientjes Subject: Re: [PATCH -v2 -mm] add extra free kbytes tunable In-Reply-To: <20110901145819.4031ef7c.akpm@linux-foundation.org> Message-ID: References: <20110901105208.3849a8ff@annuminas.surriel.com> <20110901100650.6d884589.rdunlap@xenotime.net> <20110901152650.7a63cb8b@annuminas.surriel.com> <20110901145819.4031ef7c.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Rik van Riel , Randy Dunlap , Satoru Moriya , linux-kernel@vger.kernel.org, linux-mm@kvack.org, lwoodman@redhat.com, Seiji Aguchi , hughd@google.com, hannes@cmpxchg.org On Thu, 1 Sep 2011, Andrew Morton wrote: > > Add a userspace visible knob > > argh. Fear and hostility at new knobs which need to be maintained for > ever, even if the underlying implementation changes. > Do we really need to maintain tunables that lose their purpose either because the implementation changes or is patched to fix the issue that the tunable was intended to address without requiring it? Are there really userspace tools written to not be able to handle -ENOENT when one of these gets removed? > > It may also be useful to reduce the memory use of virtual > > machines (temporarily?), in a way that does not cause memory > > fragmentation like ballooning does. > > Maybe. You need to alter the setting, then somehow persuade all the > targeted kswapd's to start running, then somehow determine that they've > done their thing, then unalter the /proc setting. Not the best API > we've ever designed ;) > And, unfortunately, this could have negative effects if using cpusets and/or mempolicies since this is global across all zones such that jobs that do not require such "extra" memory would be unfairly penalized with work incurred by additional reclaim they don't need. And if the job is constrained to a memory cgroup, there's no guarantee it will reclaim back to these altered watermarks. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org