From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx203.postini.com [74.125.245.203]) by kanga.kvack.org (Postfix) with SMTP id 406086B0044 for ; Tue, 6 Nov 2012 15:12:22 -0500 (EST) Date: Tue, 6 Nov 2012 12:12:20 -0800 From: Andrew Morton Subject: Re: [PATCH 2/2 v2] mm: print out information of file affected by memory error Message-Id: <20121106121220.d14696ac.akpm@linux-foundation.org> In-Reply-To: <1352178473-7217-1-git-send-email-n-horiguchi@ah.jp.nec.com> References: <20121105140154.fce89f05.akpm@linux-foundation.org> <1352178473-7217-1-git-send-email-n-horiguchi@ah.jp.nec.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Naoya Horiguchi Cc: Tony Luck , Andi Kleen , Wu Fengguang , Ingo Molnar , Jun'ichi Nomura , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Jan Kara On Tue, 6 Nov 2012 00:07:53 -0500 Naoya Horiguchi wrote: > On Mon, Nov 05, 2012 at 02:01:54PM -0800, Andrew Morton wrote: > > On Fri, 2 Nov 2012 12:33:13 -0400 > > Naoya Horiguchi wrote: > > > > > Printing out the information about which file can be affected by a > > > memory error in generic_error_remove_page() is helpful for user to > > > estimate the impact of the error. > > > > > > Changelog v2: > > > - dereference mapping->host after if (!mapping) check for robustness > > > > > > ... > > > > > > --- v3.7-rc3.orig/mm/truncate.c > > > +++ v3.7-rc3/mm/truncate.c > > > @@ -151,14 +151,20 @@ int truncate_inode_page(struct address_space *mapping, struct page *page) > > > */ > > > int generic_error_remove_page(struct address_space *mapping, struct page *page) > > > { > > > + struct inode *inode; > > > + > > > if (!mapping) > > > return -EINVAL; > > > + inode = mapping->host; > > > /* > > > * Only punch for normal data pages for now. > > > * Handling other types like directories would need more auditing. > > > */ > > > - if (!S_ISREG(mapping->host->i_mode)) > > > + if (!S_ISREG(inode->i_mode)) > > > return -EIO; > > > + pr_info("MCE %#lx: file info pgoff:%lu, inode:%lu, dev:%s\n", > > > + page_to_pfn(page), page_index(page), > > > + inode->i_ino, inode->i_sb->s_id); > > > return truncate_inode_page(mapping, page); > > > } > > > EXPORT_SYMBOL(generic_error_remove_page); > > > > A couple of things. > > > > - I worry that if a hardware error occurs, it might affect a large > > amount of memory all at the same time. For example, if a 4G memory > > block goes bad, this message will be printed a million times? > > If the error on 4G memory block triggered by SRAO MCE and these 1M pages > are all pagecache pages, the answer is yes. Well that's bad. > But I think that if it's a whole DIMM error, it should be reported by > another type of MCE than SRAO, so printing a million times seems to be > unlikely to happen. "should be" and "unlikely" aren't very reassuring things to hear! Emitting a million lines into syslog is pretty poor behaviour and should be reliably avoided. > > - hard-wiring "MCE" in here seems a bit of a layering violation? > > What right does the generic, core .error_remove_page() implementation > > have to assume that it was called because of an MCE? > > OK, we need not assume that. I change "MCE " prefix to more specific > one like "Memory error ". > > > Many CPU types don't eveh have such a thing? > > No. At least currently, only SRAO MCE triggers memory_failure() and > it's defined only on some newest highend models of Intel CPUs. Again, your reply is full of assumptions about one particualar implementation on one particular CPU. But this is generic, cross-architecture code! Now, it's pretty harmless to make these assumptions at this time. But this new code will need to redone if/when other CPU types come along, and because there's a printk in there, that rework will cause user-visible changes in kernel behaviour. It would be best if we can just avoid the problem on day one. Maybe move the printk into x86-specific code? And just one printk please - not a million! -- 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