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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 BEAABC433DB for ; Tue, 16 Mar 2021 23:33:15 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 3C6FC64EF3 for ; Tue, 16 Mar 2021 23:33:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3C6FC64EF3 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 902736B0036; Tue, 16 Mar 2021 19:33:13 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8D9586B006C; Tue, 16 Mar 2021 19:33:13 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 77C2B6B006E; Tue, 16 Mar 2021 19:33:13 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 5BE4D6B0036 for ; Tue, 16 Mar 2021 19:33:13 -0400 (EDT) Received: from smtpin25.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 18EED180AD837 for ; Tue, 16 Mar 2021 23:33:13 +0000 (UTC) X-FDA: 77927340666.25.BF1A18D Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf03.hostedemail.com (Postfix) with ESMTP id 2E2F2C0001F7 for ; Tue, 16 Mar 2021 23:33:12 +0000 (UTC) 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> X-Stat-Signature: oiocw5ryneo5pynqzr67i1a9g7eyfuo3 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 2E2F2C0001F7 Received-SPF: none (infradead.org>: No applicable sender policy available) receiver=imf03; identity=mailfrom; envelope-from=""; helo=casper.infradead.org; client-ip=90.155.50.34 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615937592-715788 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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?