From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755192Ab0BOQY6 (ORCPT ); Mon, 15 Feb 2010 11:24:58 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:39478 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753351Ab0BOQY4 (ORCPT ); Mon, 15 Feb 2010 11:24:56 -0500 Date: Mon, 15 Feb 2010 11:24:53 -0500 From: Christoph Hellwig To: Nick Piggin Cc: Jan Kara , Andrew Morton , LKML , fengguang.wu@intel.com Subject: Re: [PATCH 2/3] mm: Implement writeback livelock avoidance using page tagging Message-ID: <20100215162453.GA6477@infradead.org> References: <1265929584-5080-1-git-send-email-jack@suse.cz> <1265929584-5080-3-git-send-email-jack@suse.cz> <20100212113955.4c023130.akpm@linux-foundation.org> <20100215154751.GG3434@quack.suse.cz> <20100215162127.GU5723@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100215162127.GU5723@laptop> User-Agent: Mutt/1.5.19 (2009-01-05) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 16, 2010 at 03:21:27AM +1100, Nick Piggin wrote: > Also, I wonder what you think about leaving the tags dangling when > the loop bails out early? I have a *slight* concern about this > because previously we never have a tag set when radix_tree_delete > is called. I actually had a bug in that code in earlier versions > of rcu radix tree that only got found by the user test harness. > And another slight concern that it is just a bit ugly to leave the > tag. But I can accept that lower CPU overhead trumps ugliness :) The XFS inode cache calls radix_tree_delete with a tag set, and interestingly enough we're trying to catch a very weird bug in that area currently, which seems more or less directly related to the use of tags. But we also had a real locking bug related to tags, so I'm not yet sure what the issue is back until I hear back from the bug reported and reproducer.