From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id BA1259000BD for ; Mon, 20 Jun 2011 13:34:59 -0400 (EDT) Message-ID: <4DFF84BB.3050209@redhat.com> Date: Tue, 21 Jun 2011 01:34:51 +0800 From: Cong Wang MIME-Version: 1.0 Subject: Re: [PATCH 1/3] mm: completely disable THP by transparent_hugepage=never References: <1308587683-2555-1-git-send-email-amwang@redhat.com> <20110620165844.GA9396@suse.de> <4DFF7E3B.1040404@redhat.com> <4DFF7F0A.8090604@redhat.com> <4DFF8106.8090702@redhat.com> <4DFF8327.1090203@redhat.com> In-Reply-To: <4DFF8327.1090203@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Rik van Riel Cc: Mel Gorman , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Andrea Arcangeli , Johannes Weiner , KAMEZAWA Hiroyuki , linux-mm@kvack.org ao? 2011a1'06ae??21ae?JPY 01:28, Rik van Riel a??e??: > On 06/20/2011 01:19 PM, Cong Wang wrote: >> ao? 2011a1'06ae??21ae?JPY 01:10, Rik van Riel a??e??: >>> On 06/20/2011 01:07 PM, Cong Wang wrote: >>>> ao? 2011a1'06ae??21ae?JPY 00:58, Mel Gorman a??e??: >>>>> On Tue, Jun 21, 2011 at 12:34:28AM +0800, Amerigo Wang wrote: >>>>>> transparent_hugepage=never should mean to disable THP completely, >>>>>> otherwise we don't have a way to disable THP completely. >>>>>> The design is broken. >>>>>> >>>>> >>>>> I don't get why it's broken. Why would the user be prevented from >>>>> enabling it at runtime? >>>>> >>>> >>>> We need to a way to totally disable it, right? Otherwise, when I >>>> configure >>>> THP in .config, I always have THP initialized even when I pass "=never". >>>> >>>> For me, if you don't provide such way to disable it, it is not flexible. >>>> >>>> I meet this problem when I try to disable THP in kdump kernel, there is >>>> no user of THP in kdump kernel, THP is a waste for kdump kernel. This is >>>> why I need to find a way to totally disable it. >>> >>> What you have not explained yet is why having THP >>> halfway initialized (but not used, and without a >>> khugepaged thread) is a problem at all. >>> >>> Why is it a problem for you? >> >> It occupies some memory, memory is valuable in kdump kernel (usually >> only 128M). :) Since I am sure no one will use it, why do I still need >> to initialize it at all? > > Lets take a look at how much memory your patches end > up saving. > > By bailing out earlier in hugepage_init, you end up > saving 3 sysfs objects, one slab cache and a hash > table with 1024 pointers. That's a total of maybe > 10kB of memory on a 64 bit system. > > I'm not convinced that a 10kB memory reduction is > worth the price of never being able to enable > transparent hugepages when a system is booted with > THP disabled... > Even if it is really 10K, why not save it since it doesn't much effort to make this. ;) Not only memory, but also time, this could also save a little time to initialize the kernel. For me, the more serious thing is the logic, there is no way to totally disable it as long as I have THP in .config currently. This is why I said the design is broken. Thanks. -- 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