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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <163456861570.2614702.14754548462706508617.stgit@warthog.procyon.org.uk> To: Jeff Layton Cc: dhowells@redhat.com, linux-cachefs@redhat.com, ceph-devel@vger.kernel.org, linux-afs@lists.infradead.org, Anna Schumaker , linux-nfs@vger.kernel.org, Kent Overstreet , linux-mm@kvack.org, Matthew Wilcox , linux-fsdevel@vger.kernel.org, Dave Wysochanski , Marc Dionne , Trond Myklebust , Shyam Prasad N , Eric Van Hensbergen , v9fs-developer@lists.sourceforge.net, linux-cifs@vger.kernel.org, Latchesar Ionkov , Steve French , Al Viro , Dominique Martinet , Ilya Dryomov , Trond Myklebust , Omar Sandoval , Linus Torvalds , linux-kernel@vger.kernel.org Subject: Re: [PATCH 00/67] fscache: Rewrite index API and management system MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <2972093.1634670049.1@warthog.procyon.org.uk> Date: Tue, 19 Oct 2021 20:00:49 +0100 Message-ID: <2972094.1634670049@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: E39A990000BB X-Stat-Signature: 87fuedk4jko6idd98f5hwxjqetyjrs9t Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="Z/8hcUNm"; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf23.hostedemail.com: domain of dhowells@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=dhowells@redhat.com X-HE-Tag: 1634670077-521275 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: Jeff Layton wrote: > Given the indexing changes, what sort of behavior should we expect when > upgrading from old-style to new-style indexes? Do they just not match, > and we end up downloading new copies of all the data and the old stale > stuff eventually gets culled? Correct: they don't match. The names of the directories and files will be quite different - and so will the attached xattrs. However, no filesystems currently store locally-modified data in the cache, so you shouldn't lose any data after upgrading. > Ditto for downgrades -- can we expect sane behavior if someone runs an > old kernel on top of an existing fscache that was populated by a new > kernel? Correct. With this branch, filesystems now store locally-modified data into the cache - but they also upload it to the server at the same time. If there's a disagreement between what's in the cache and what's on the server with this branch, the cache is discarded, so simply discarding the cache on a download shouldn't be a problem. It's currently operating as a write-through cache, not a write-back cache. That will change if I get round to implementing disconnected operation, but it's not there yet. David