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 ESMTP id 3F8C48D0039 for ; Thu, 3 Feb 2011 16:22:24 -0500 (EST) Received: from wpaz29.hot.corp.google.com (wpaz29.hot.corp.google.com [172.24.198.93]) by smtp-out.google.com with ESMTP id p13LMLk2009174 for ; Thu, 3 Feb 2011 13:22:21 -0800 Received: from pzk37 (pzk37.prod.google.com [10.243.19.165]) by wpaz29.hot.corp.google.com with ESMTP id p13LMJcY004879 (version=TLSv1/SSLv3 cipher=RC4-MD5 bits=128 verify=NOT) for ; Thu, 3 Feb 2011 13:22:20 -0800 Received: by pzk37 with SMTP id 37so362945pzk.12 for ; Thu, 03 Feb 2011 13:22:19 -0800 (PST) Date: Thu, 3 Feb 2011 13:22:14 -0800 (PST) From: David Rientjes 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> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michael J Wolf , Andrea Arcangeli 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 -- 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