From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta8.messagelabs.com (mail6.bemta8.messagelabs.com [216.82.243.55]) by kanga.kvack.org (Postfix) with ESMTP id 15E7B9000BD for ; Mon, 20 Jun 2011 13:28:13 -0400 (EDT) Message-ID: <4DFF8327.1090203@redhat.com> Date: Mon, 20 Jun 2011 13:28:07 -0400 From: Rik van Riel 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> In-Reply-To: <4DFF8106.8090702@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Cong Wang Cc: Mel Gorman , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Andrea Arcangeli , Johannes Weiner , KAMEZAWA Hiroyuki , linux-mm@kvack.org 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... -- 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