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 BEE8D9000BD for ; Mon, 20 Jun 2011 13:23:33 -0400 (EDT) Message-ID: <4DFF8207.5080700@redhat.com> Date: Tue, 21 Jun 2011 01:23:19 +0800 From: Cong Wang MIME-Version: 1.0 Subject: Re: [PATCH 2/3] mm: make the threshold of enabling THP configurable References: <1308587683-2555-1-git-send-email-amwang@redhat.com> <1308587683-2555-2-git-send-email-amwang@redhat.com> <1308589163.11430.245.camel@nimitz> In-Reply-To: <1308589163.11430.245.camel@nimitz> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Andrea Arcangeli , Mel Gorman , Benjamin Herrenschmidt , Rik van Riel , Johannes Weiner , KAMEZAWA Hiroyuki , linux-mm@kvack.org ao? 2011a1'06ae??21ae?JPY 00:59, Dave Hansen a??e??: > On Tue, 2011-06-21 at 00:34 +0800, Amerigo Wang wrote: >> +config TRANSPARENT_HUGEPAGE_THRESHOLD >> + depends on TRANSPARENT_HUGEPAGE >> + int "The minimal threshold of enabling Transparent Hugepage" >> + range 512 8192 >> + default "512" >> + help >> + The threshold of enabling Transparent Huagepage automatically, >> + in Mbytes, below this value, Transparent Hugepage will be disabled >> + by default during boot. > > It makes some sense to me that there would _be_ a threshold, simply > because you need some space to defragment things. But, I can't imagine > any kind of user having *ANY* kind of idea what to set this to. Could > we add some text to this? Maybe: > > Transparent hugepages are created by moving other pages out of > the way to create large, contiguous swaths of free memory. > However, some memory on a system can not be easily moved. It is > likely on small systems that this unmovable memory will occupy a > large portion of total memory, which makes even attempting to > create transparent hugepages very expensive. > > If you are unsure, set this to the smallest possible value. > > To override this at boot, use the $FOO boot command-line option. > Yeah, I totally agree to improve the help message as you said, please forgive a non-English speaker. ;) > I'm also not sure putting a ceiling on this makes a lot of sense. > What's the logic behind that? I know it would be a mess to expose it to > users, but shouldn't this be a per-zone limit, logically? Seems like a > 8GB system would have similar issues to a two-numa-node 16GB system. > I am not sure about this, since I am new to THP, I just replaced the hard-code 512 with a Kconfig var. But I am certainly open to improve this as you said if Andrea agrees. 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