From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.6 required=5.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI, T_DKIM_INVALID autolearn=unavailable autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id EBD677D2EE for ; Fri, 31 Aug 2018 14:31:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727631AbeHaSiz (ORCPT ); Fri, 31 Aug 2018 14:38:55 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:46362 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727572AbeHaSiz (ORCPT ); Fri, 31 Aug 2018 14:38:55 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=fMCemegQnyuRXe3rpJk0Tz/7i5F8/97y2iTDT7TwqEI=; b=qrHL2/mtkVyQ5+fM3HimAU9Wh zndRRMWqAPECe7OcJ12nNsLtpHIO+/241+5kUuNqmXxK4X/bOCJfwDlau9qe/s2DdkNc1In7J4YzU zWpflyxN0VGGT/LK+8pAK0QAqPdeRBAsf7N4CpYevm5XvWSbrgT7YbdCe8JDZ7jeS2O7PnGuVKO6r Qb8iVv7eiGtV/sNUiWyIYBFK9o19M/hXp+2YyRazhER01+qpmS8clz4ZrlExy+cs+y4l0JXRfQ6s6 lUUly45zZMAQC987BB+42B6R5DwlRJfjUsuBLkZlrCAMJ3WyJaYlWGcylIzoTaeymRwiE4OI8BkKF iJwubyLUQ==; Received: from willy by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1fvkRx-00050N-2U; Fri, 31 Aug 2018 14:31:01 +0000 Date: Fri, 31 Aug 2018 07:31:00 -0700 From: Matthew Wilcox To: Dave Chinner Cc: Waiman Long , Alexander Viro , Jonathan Corbet , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, "Luis R. Rodriguez" , Kees Cook , Linus Torvalds , Jan Kara , "Paul E. McKenney" , Andrew Morton , Ingo Molnar , Miklos Szeredi , Larry Woodman , James Bottomley , "Wangkai (Kevin C)" , Michal Hocko Subject: Re: [PATCH 1/2] fs/dcache: Track & report number of negative dentries Message-ID: <20180831143100.GA6379@bombadil.infradead.org> References: <1535476780-5773-1-git-send-email-longman@redhat.com> <1535476780-5773-2-git-send-email-longman@redhat.com> <20180829001153.GD1572@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180829001153.GD1572@dastard> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Wed, Aug 29, 2018 at 10:11:53AM +1000, Dave Chinner wrote: > > +++ b/Documentation/sysctl/fs.txt > > @@ -63,19 +63,26 @@ struct { > > int nr_unused; > > int age_limit; /* age in seconds */ > > int want_pages; /* pages requested by system */ > > - int dummy[2]; > > + int nr_negative; /* # of unused negative dentries */ > > + int dummy; > > } dentry_stat = {0, 0, 45, 0,}; > > That's not a backwards compatible ABI change. Those dummy fields > used to represent some metric we no longer calculate, and there are > probably still monitoring apps out there that think they still have > the old meaning. i.e. they are still visible to userspace: I believe you are incorrect. dentry_stat was introduced in 2.1.60 with this hunk: +struct { + int nr_dentry; + int nr_unused; + int age_limit; /* age in seconds */ + int want_pages; /* pages requested by system */ + int dummy[2]; +} dentry_stat = {0, 0, 45, 0,}; + Looking through the rest of the dentry_stat changes in the 2.1.60 release, it's not replacing anything, it's adding new information.