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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AD622C433F5 for ; Fri, 29 Oct 2021 18:52:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 975FC60F22 for ; Fri, 29 Oct 2021 18:52:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230442AbhJ2Sya (ORCPT ); Fri, 29 Oct 2021 14:54:30 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:38664 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230273AbhJ2Sy2 (ORCPT ); Fri, 29 Oct 2021 14:54:28 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1635533518; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/vX1aXmgWDOmHXytC/xtmTFfVJMO+hskcobUwtJeMmI=; b=H8seKFppfj7RTniLl8qMPFbNHiBTU/Cx6TGPmDtuYq7STB6GNxpFB/+QjX7t8a4wzfU6SA p2JWZriQeHgAGkSlA3V11yBruuF+HkBR3tgbxZC3CPVge2OsRYNbzZ+EmYgxhDc7oM3GWc Kh0dM4UchE9yJKCS4JjlS00zJFUzE8U= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-475-p1zGB8TrMduU9GKrjace1w-1; Fri, 29 Oct 2021 14:51:55 -0400 X-MC-Unique: p1zGB8TrMduU9GKrjace1w-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 008188F515; Fri, 29 Oct 2021 18:51:53 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.33.36.19]) by smtp.corp.redhat.com (Postfix) with ESMTP id E18845D6CF; Fri, 29 Oct 2021 18:51:34 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <163551653404.1877519.12363794970541005441.stgit@warthog.procyon.org.uk> <1889041.1635530124@warthog.procyon.org.uk> To: Linus Torvalds Cc: dhowells@redhat.com, Trond Myklebust , Anna Schumaker , Steve French , Dominique Martinet , v9fs-developer@lists.sourceforge.net, CIFS , Trond Myklebust , "open list:NFS, SUNRPC, AND..." , linux-cachefs@redhat.com, Dave Wysochanski , Shyam Prasad N , Jeff Layton , Matthew Wilcox , Alexander Viro , linux-afs@lists.infradead.org, ceph-devel@vger.kernel.org, linux-fsdevel , Linux Kernel Mailing List Subject: Re: [PATCH v4 00/10] fscache: Replace and remove old I/O API MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <1891410.1635533494.1@warthog.procyon.org.uk> Content-Transfer-Encoding: quoted-printable Date: Fri, 29 Oct 2021 19:51:34 +0100 Message-ID: <1891411.1635533494@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org Linus Torvalds wrote: > But: > = > > However, if you would rather I just removed all of fscache and (most o= f[*]) > > cachefiles, that I can do. > = > I assume and think that if you just do that part first, then the > "convert to netfslib" of afs and ceph at that later stage will mean > that the fallback code will never be needed? The netfslib coversions for afs and ceph are already in your tree and I ha= ve a patch here to do that for 9p (if you're willing to take that in the upcomi= ng merge window?). The issue is cifs[*] and nfs. I could leave caching in those disabled, pending approved patches for those filesystems. This would mean that I wouldn't need the fallback code. An alternative is that I could move the "fallback" code into fs/nfs/fscach= e.c and fs/cifs/fscache.c if that would be easier and merge it into the functi= ons there. The problem will come when the cache wants to do I/O in larger uni= ts than page size to suit its own block size[**]. David [*] As it happens, it turns out that cifs seems to have a bug in it that causes the entire cache for a superblock to be discarded each time that superblock is mounted. [**] At some point the cache *has* to start keeping track of what data it = is holding rather than relying on bmap/SEEK_DATA/SEEK_HOLE to get round the extent-bridging problem. I'm trying to take a leaf out of the book of oth= er caching filesystems and use larger block sizes (e.g. 256K) to reduce the overhead of cache metadata.