From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id F283E6B0044 for ; Thu, 10 Dec 2009 20:29:30 -0500 (EST) Received: from m5.gw.fujitsu.co.jp ([10.0.50.75]) by fgwmail5.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id nBB1TSiJ001133 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Fri, 11 Dec 2009 10:29:28 +0900 Received: from smail (m5 [127.0.0.1]) by outgoing.m5.gw.fujitsu.co.jp (Postfix) with ESMTP id 1248845DE58 for ; Fri, 11 Dec 2009 10:29:28 +0900 (JST) Received: from s5.gw.fujitsu.co.jp (s5.gw.fujitsu.co.jp [10.0.50.95]) by m5.gw.fujitsu.co.jp (Postfix) with ESMTP id A513D45DE4E for ; Fri, 11 Dec 2009 10:29:27 +0900 (JST) Received: from s5.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s5.gw.fujitsu.co.jp (Postfix) with ESMTP id 6981D1DB805D for ; Fri, 11 Dec 2009 10:29:27 +0900 (JST) Received: from m107.s.css.fujitsu.com (m107.s.css.fujitsu.com [10.249.87.107]) by s5.gw.fujitsu.co.jp (Postfix) with ESMTP id 02ABFE1800F for ; Fri, 11 Dec 2009 10:29:27 +0900 (JST) Date: Fri, 11 Dec 2009 10:26:29 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [RFC mm][PATCH 2/5] percpu cached mm counter Message-Id: <20091211102629.4fe1ac43.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <28c262360912101725ydb0a0d9i12a91c1d4fe57672@mail.gmail.com> References: <20091210163115.463d96a3.kamezawa.hiroyu@jp.fujitsu.com> <20091210163448.338a0bd2.kamezawa.hiroyu@jp.fujitsu.com> <28c262360912101640y4b90db76w61a7a5dab5f8e796@mail.gmail.com> <20091211095159.6472a009.kamezawa.hiroyu@jp.fujitsu.com> <28c262360912101725ydb0a0d9i12a91c1d4fe57672@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org To: Minchan Kim Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , cl@linux-foundation.org, "akpm@linux-foundation.org" , mingo@elte.hu List-ID: On Fri, 11 Dec 2009 10:25:03 +0900 Minchan Kim wrote: > On Fri, Dec 11, 2009 at 9:51 AM, KAMEZAWA Hiroyuki > wrote: > > On Fri, 11 Dec 2009 09:40:07 +0900 > > Minchan Kim wrote: > >> >A static inline unsigned long get_mm_counter(struct mm_struct *mm, int member) > >> > A { > >> > - A A A return (unsigned long)atomic_long_read(&(mm)->counters[member]); > >> > + A A A long ret; > >> > + A A A /* > >> > + A A A A * Because this counter is loosely synchronized with percpu cached > >> > + A A A A * information, it's possible that value gets to be minus. For user's > >> > + A A A A * convenience/sanity, avoid returning minus. > >> > + A A A A */ > >> > + A A A ret = atomic_long_read(&(mm)->counters[member]); > >> > + A A A if (unlikely(ret < 0)) > >> > + A A A A A A A return 0; > >> > + A A A return (unsigned long)ret; > >> > A } > >> > >> Now, your sync point is only task switching time. > >> So we can't show exact number if many counting of mm happens > >> in short time.(ie, before context switching). > >> It isn't matter? > >> > > I think it's not a matter from 2 reasons. > > > > 1. Now, considering servers which requires continuous memory usage monitoring > > as ps/top, when there are 2000 processes, "ps -elf" takes 0.8sec. > > Because system admins know that gathering process information consumes > > some amount of cpu resource, they will not do that so frequently.(I hope) > > > > 2. When chains of page faults occur continously in a period, the monitor > > of memory usage just see a snapshot of current numbers and "snapshot of what > > moment" is at random, always. No one can get precise number in that kind of situation. > > > > Yes. I understand that. > > But we did rss updating as batch until now. > It was also stale. Just only your patch make stale period longer. > Hmm. I hope people don't expect mm count is precise. > I hope so, too... > I saw the many people believed sanpshot of mm counting is real in > embedded system. > They want to know the exact memory usage in system. > Maybe embedded system doesn't use SPLIT_LOCK so that there is no regression. > > At least, I would like to add comment "It's not precise value." on > statm's Documentation. Ok, I'll will do. > Of course, It's off topic. :) > > Thanks for commenting. Kame. Thank you for review. Regards, -Kame -- 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/ . Don't email: email@kvack.org