From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 20B71C433E0 for ; Tue, 16 Mar 2021 23:34:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ECEC664EF6 for ; Tue, 16 Mar 2021 23:34:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229548AbhCPXdp (ORCPT ); Tue, 16 Mar 2021 19:33:45 -0400 Received: from casper.infradead.org ([90.155.50.34]:44504 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229754AbhCPXdU (ORCPT ); Tue, 16 Mar 2021 19:33:20 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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; bh=ugD/jJZR2x4PlwFOPLM1Z8A1WHyvGKetbXN+yb06xfM=; b=OX7RitBwZ7oc3GO38XAXfxdoij vfKiFKYeao1v7N+9Nx7PTu9Z61XntTa7fENRJtgQ3CooWOi6pFGDLJfOCWvQSPDMt18AuEvLmsG/t w8/YLaN0lddz/EqtFRwAlhyPeA9k4RDxbsO5JOnmoGPMQvITYjkp3S7vUIHxpsbZNUio5Ko0ZVsEk spv1+ANWI7xmV3T6aAKDnp+5lQTDx1iFWg+gZ2u+pQegvhUWAjAjQXwbLjDk4o9yLmXkUmEvsqvJb 3MnhN12ApsM12ymiXHH0JigGgpTf+2cbMmzeHJageIJBcRi9noxplnjX/iPmBZqWg1lpllSgZWaT2 pwg8kffg==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lMJB6-000lEX-7N; Tue, 16 Mar 2021 23:32:48 +0000 Date: Tue, 16 Mar 2021 23:32:44 +0000 From: Matthew Wilcox To: David Howells Cc: Trond Myklebust , Anna Schumaker , Steve French , Dominique Martinet , Linus Torvalds , Christoph Hellwig , Alexander Viro , linux-mm@kvack.org, linux-cachefs@redhat.com, linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, Jeff Layton , David Wysochanski , linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 02/28] mm: Add an unlock function for PG_private_2/PG_fscache Message-ID: <20210316233244.GE3420@casper.infradead.org> References: <20210316190707.GD3420@casper.infradead.org> <161539526152.286939.8589700175877370401.stgit@warthog.procyon.org.uk> <161539528910.286939.1252328699383291173.stgit@warthog.procyon.org.uk> <3313319.1615927080@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3313319.1615927080@warthog.procyon.org.uk> Precedence: bulk List-ID: X-Mailing-List: ceph-devel@vger.kernel.org On Tue, Mar 16, 2021 at 08:38:00PM +0000, David Howells wrote: > Matthew Wilcox wrote: > > > So ... a page with both flags cleared should have a refcount of N. > > A page with one or both flags set should have a refcount of N+1. > > ... > > How is a poor filesystem supposed to make that true? Also btrfs has this > > problem since it uses private_2 for its own purposes. > > It's simpler if it's N+2 for both patches set. Btw, patch 13 adds that - and > possibly that should be merged into an earlier patch. So ... static inline int page_has_private(struct page *page) { unsigned long flags = page->flags; return ((flags >> PG_private) & 1) + ((flags >> PG_private_2) & 1); } perhaps?