From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id 746D36B004D for ; Tue, 1 Sep 2009 02:47:07 -0400 (EDT) Date: Tue, 1 Sep 2009 14:46:52 +0800 From: Wu Fengguang Subject: Re: [RFC][PATCH 0/4] memcg: add support for hwpoison testing Message-ID: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090901113214.60e7ae32.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki 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, 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; } > 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.. Cheers, Fengguang -- 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