From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752056Ab1BAJ6O (ORCPT ); Tue, 1 Feb 2011 04:58:14 -0500 Received: from zene.cmpxchg.org ([85.214.230.12]:35663 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750859Ab1BAJ6N (ORCPT ); Tue, 1 Feb 2011 04:58:13 -0500 Date: Tue, 1 Feb 2011 10:58:08 +0100 From: Johannes Weiner 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 Message-ID: <20110201095808.GG19534@cmpxchg.org> References: <20110201003357.D6F0BE0D@kernel> <20110201003358.98826457@kernel> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110201003358.98826457@kernel> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 31, 2011 at 04:33:58PM -0800, 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. > > Signed-off-by: Dave Hansen Acked-by: Johannes Weiner