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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <20210316190707.GD3420@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> To: Matthew Wilcox Cc: dhowells@redhat.com, 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 MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <3313318.1615927080.1@warthog.procyon.org.uk> Date: Tue, 16 Mar 2021 20:38:00 +0000 Message-ID: <3313319.1615927080@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Stat-Signature: 5r8dopu5cijkacfa3m19qq9r6owga9q1 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 4251BC0007E4 Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf14; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=170.10.133.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615927093-335883 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: 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. David