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=-0.8 required=3.0 tests=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 869CAC3A59B for ; Fri, 30 Aug 2019 16:17:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 562612342C for ; Fri, 30 Aug 2019 16:17:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727434AbfH3QR5 (ORCPT ); Fri, 30 Aug 2019 12:17:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46336 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727135AbfH3QR4 (ORCPT ); Fri, 30 Aug 2019 12:17:56 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 706A1A36EE1; Fri, 30 Aug 2019 16:17:56 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-120-255.rdu2.redhat.com [10.10.120.255]) by smtp.corp.redhat.com (Postfix) with ESMTP id 593541001284; Fri, 30 Aug 2019 16:17:52 +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: <20190829071312.GE11909@lst.de> References: <20190829071312.GE11909@lst.de> <20190820115731.bed7gwfygk66nj43@pegasus.maiolino.io> <20190808082744.31405-1-cmaiolino@redhat.com> <20190808082744.31405-3-cmaiolino@redhat.com> <20190814111535.GC1885@lst.de> <7003.1566305430@warthog.procyon.org.uk> To: Christoph Hellwig Cc: dhowells@redhat.com, Carlos Maiolino , linux-fsdevel@vger.kernel.org, adilger@dilger.ca, jaegeuk@kernel.org, darrick.wong@oracle.com, miklos@szeredi.hu, rpeterso@redhat.com, linux-xfs@vger.kernel.org Subject: Re: [PATCH 2/9] cachefiles: drop direct usage of ->bmap method. MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <2585.1567181871.1@warthog.procyon.org.uk> Date: Fri, 30 Aug 2019 17:17:51 +0100 Message-ID: <2587.1567181871@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.68]); Fri, 30 Aug 2019 16:17:56 +0000 (UTC) Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org Christoph Hellwig wrote: > Not related to this patch, but using iov_iter with dio is trivial, what > is the blocker therere? The usual: time. The change as a whole is not actually trivial since it will involve completely overhauling the fscache data API and how the filesystems use it - and then having cachefiles perform the DIO asynchronously as per Trond's requirements for using fscache with NFS. I also need to work out how I'm going to do data/hole detection. Can I set, say, O_NOREADHOLE and then expect the DIO to stop early with a short read? Or do I need to use SEEK_DATA/SEEK_HOLE in advance to define the occupied regions? Maybe a better way would be to take a leaf out of the book of OpenAFS and suchlike and keep a parallel file that tracks the occupancy of a cache object (eg. a bitmap with 1 bit per 64k block) - but that the synchronisation and performance issues. David