From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753256Ab1BCVWZ (ORCPT ); Thu, 3 Feb 2011 16:22:25 -0500 Received: from smtp-out.google.com ([216.239.44.51]:18349 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753022Ab1BCVWX (ORCPT ); Thu, 3 Feb 2011 16:22:23 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=date:from:x-x-sender:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version:content-type; b=MqXR8f0KR5cYP9Ymk1Vj664NbI5YSW6jN9/fLP55hkarXCmCIij8YV09AQRmN8i94A EhM9th9aBFsEiHX/7Ahw== Date: Thu, 3 Feb 2011 13:22:14 -0800 (PST) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Dave Hansen cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michael J Wolf , Andrea Arcangeli Subject: Re: [RFC][PATCH 1/6] count transparent hugepage splits In-Reply-To: <20110201003358.98826457@kernel> Message-ID: References: <20110201003357.D6F0BE0D@kernel> <20110201003358.98826457@kernel> 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 Mon, 31 Jan 2011, Dave Hansen wrote: > > The khugepaged process collapses transparent hugepages for us. Whenever > it collapses a page into a transparent hugepage, we increment a nice > global counter exported in sysfs: > > /sys/kernel/mm/transparent_hugepage/khugepaged/pages_collapsed > > But, transparent hugepages also get broken down in quite a few > places in the kernel. We do not have a good idea how how many of > those collpased pages are "new" versus how many are just fixing up > spots that got split a moment before. > > Note: "splits" and "collapses" are opposites in this context. > > This patch adds a new sysfs file: > > /sys/kernel/mm/transparent_hugepage/pages_split > > It is global, like "pages_collapsed", and is incremented whenever any > transparent hugepage on the system has been broken down in to normal > PAGE_SIZE base pages. This way, we can get an idea how well khugepaged > is keeping up collapsing pages that have been split. > > I put it under /sys/kernel/mm/transparent_hugepage/ instead of the > khugepaged/ directory since it is not strictly related to > khugepaged; it can get incremented on pages other than those > collapsed by khugepaged. > > The variable storing this is a plain integer. I needs the same > amount of locking that 'khugepaged_pages_collapsed' has, for > instance. i.e. no global locking, but we've accepted the occassional off-by-one error (even though splitting of hugepages isn't by any means lightning fast and the overhead of atomic ops would be negligible). > Signed-off-by: Dave Hansen Acked-by: David Rientjes