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 3DA6F6B004D for ; Tue, 1 Sep 2009 03:14:35 -0400 (EDT) Received: from m1.gw.fujitsu.co.jp ([10.0.50.71]) by fgwmail7.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id n817EbZq003766 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Tue, 1 Sep 2009 16:14:38 +0900 Received: from smail (m1 [127.0.0.1]) by outgoing.m1.gw.fujitsu.co.jp (Postfix) with ESMTP id 8AB1E45DE6C for ; Tue, 1 Sep 2009 16:14:37 +0900 (JST) Received: from s1.gw.fujitsu.co.jp (s1.gw.fujitsu.co.jp [10.0.50.91]) by m1.gw.fujitsu.co.jp (Postfix) with ESMTP id 3A76545DE66 for ; Tue, 1 Sep 2009 16:14:37 +0900 (JST) Received: from s1.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s1.gw.fujitsu.co.jp (Postfix) with ESMTP id D56F51DB8048 for ; Tue, 1 Sep 2009 16:14:36 +0900 (JST) Received: from ml13.s.css.fujitsu.com (ml13.s.css.fujitsu.com [10.249.87.103]) by s1.gw.fujitsu.co.jp (Postfix) with ESMTP id D53F21DB804E for ; Tue, 1 Sep 2009 16:14:30 +0900 (JST) Date: Tue, 1 Sep 2009 16:12:28 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [RFC][PATCH 0/4] memcg: add support for hwpoison testing Message-Id: <20090901161228.9fb33234.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20090901064652.GA20342@localhost> References: <20090831102640.092092954@intel.com> <20090901084626.ac4c8879.kamezawa.hiroyu@jp.fujitsu.com> <20090901022514.GA11974@localhost> <20090901113214.60e7ae32.kamezawa.hiroyu@jp.fujitsu.com> <20090901064652.GA20342@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Wu Fengguang Cc: Balbir Singh , Andi Kleen , Andrew Morton , LKML , KOSAKI Motohiro , Rik van Riel , Mel Gorman , "lizf@cn.fujitsu.com" , "nishimura@mxp.nes.nec.co.jp" , "menage@google.com" , linux-mm List-ID: On Tue, 1 Sep 2009 14:46:52 +0800 Wu Fengguang wrote: > On Tue, Sep 01, 2009 at 10:32:14AM +0800, KAMEZAWA Hiroyuki wrote: > > On Tue, 1 Sep 2009 10:25:14 +0800 > > Wu Fengguang wrote: > > > > 4. I can't understand why you need this. I wonder you can get pfn via > > > > /proc//????. And this may insert HWPOISON to page-cache of shared > > > > library and "unexpected" process will be poisoned. > > > > > > Sorry I should have explained this. It's mainly for correctness. > > > When a user space tool queries the task PFNs in /proc/pid/pagemap and > > > then send to /debug/hwpoison/corrupt-pfn, there is a racy window that > > > the page could be reclaimed and allocated by some one else. It would > > > be awkward to try to pin the pages in user space. So we need the > > > guarantees provided by /debug/hwpoison/corrupt-filter-memcg, which > > > will be checked inside the page lock with elevated reference count. > > > > > > > memcg never holds refcnt for a page and the kernel::vmscan.c can reclaim > > any pages under memcg whithout checking anything related to memcg. > > *And*, your code has no "pin" code. > > This patch sed does no jobs for your concern. > > We grabbed page here, which is not in the scope of this patchset: > > static int try_memory_failure(unsigned long pfn) > { > struct page *p; > int res = -EINVAL; > > if (!pfn_valid(pfn)) > return res; > > p = pfn_to_page(pfn); > if (!get_page_unless_zero(compound_head(p))) > return res; > > lock_page_nosync(compound_head(p)); > > if (hwpoison_filter(p)) > goto out; > > res = __memory_failure(pfn, 18, > MEMORY_FAILURE_FLAG_COUNTED | > MEMORY_FAILURE_FLAG_LOCKED); > out: > unlock_page(p); > return res; > } Hmm. maybe off-topic but why lock_page() is necessary ? > > I recommend you to add > > /debug/hwpoizon/pin-pfn > > > > Then, > > echo pfn > /debug/hwpoizon/pin-pfn > > # add pfn for hwpoison debug's watch list. and elevate refcnt > > check 'pfn' is still used. > > echo pfn > /debug/hwpoison/corrupt-pfn > > # check 'watch list' and make it corrupt and release refcnt. > > or some. > > Looks like a good alternative. At least no more memcg dependency.. > My point is that memcg can show 'owner' of pages but the page may be shared with something important task _and_ if a task is migrated, its pages' memcg information is not updated now. Then, you can kill a task which is not in memcg. Then, I don't recommend to use memcg. I think you'll see too much pitfalls. Thanks, -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