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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 BF436C38BF9 for ; Mon, 24 Feb 2020 21:43:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 957C821556 for ; Mon, 24 Feb 2020 21:43:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="WER6q6aM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728145AbgBXVns (ORCPT ); Mon, 24 Feb 2020 16:43:48 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:34554 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727976AbgBXVns (ORCPT ); Mon, 24 Feb 2020 16:43:48 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Transfer-Encoding :Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description; bh=IBmpdg54DdbeZAoJdfQydcGyDg8H1e/FIpFw/vfYtE4=; b=WER6q6aMIxiEGc+j/HGcg87kgh fzNH5dUAX47ArvTEcqOgiOSjadyzvjYxi7Z+MNemow4AoVsB97AsbXwMFCWorXOXLyW4/Bi/1vxFR pekPIkO1XBmskg8wIjbG1r89NfDd26q/hqyfaI2g/8EolO9JVp55Al1+R5Mb9Co/yj7iles1i8y0+ Ogbq4hrGehMtbChyDWTVLnLZK/CEUdmMF6F7w+67mUpRFsUbz1BetpuyOeDRb0R9UTQUnw/MfxN4t On18RaxEjiVcVeDM/VtvaYZgSM8WH7HCFrdX8QnSdbWbJyOTtLdDJc38/NHqwAQoFYGr30to44pf+ HaIFogKQ==; Received: from hch by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j6LVz-0007sB-AO; Mon, 24 Feb 2020 21:43:47 +0000 Date: Mon, 24 Feb 2020 13:43:47 -0800 From: Christoph Hellwig To: Matthew Wilcox Cc: Christoph Hellwig , Johannes Thumshirn , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "linux-btrfs@vger.kernel.org" , "linux-erofs@lists.ozlabs.org" , "linux-ext4@vger.kernel.org" , "linux-f2fs-devel@lists.sourceforge.net" , "cluster-devel@redhat.com" , "ocfs2-devel@oss.oracle.com" , "linux-xfs@vger.kernel.org" Subject: Re: [PATCH v7 14/24] btrfs: Convert from readpages to readahead Message-ID: <20200224214347.GH13895@infradead.org> References: <20200219210103.32400-1-willy@infradead.org> <20200219210103.32400-15-willy@infradead.org> <20200220134849.GV24185@bombadil.infradead.org> <20200220154658.GA19577@infradead.org> <20200220155452.GX24185@bombadil.infradead.org> <20200220155727.GA32232@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200220155727.GA32232@infradead.org> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Feb 20, 2020 at 07:57:27AM -0800, Christoph Hellwig wrote: > On Thu, Feb 20, 2020 at 07:54:52AM -0800, Matthew Wilcox wrote: > > On Thu, Feb 20, 2020 at 07:46:58AM -0800, Christoph Hellwig wrote: > > > On Thu, Feb 20, 2020 at 05:48:49AM -0800, Matthew Wilcox wrote: > > > > btrfs: Convert from readpages to readahead > > > > > > > > Implement the new readahead method in btrfs. Add a readahead_page_batch() > > > > to optimise fetching a batch of pages at once. > > > > > > Shouldn't this readahead_page_batch heper go into a separate patch so > > > that it clearly stands out? > > > > I'll move it into 'Put readahead pages in cache earlier' for v8 (the > > same patch where we add readahead_page()) > > One argument for keeping it in a patch of its own is that btrfs appears > to be the only user, and Goldwyn has a WIP conversion of btrfs to iomap, > so it might go away pretty soon and we could just revert the commit. > > But this starts to get into really minor details, so I'll shut up now :) So looking at this again I have another comment and a question. First I think the implicit ARRAY_SIZE in readahead_page_batch is highly dangerous, as it will do the wrong thing when passing a pointer or function argument. Second I wonder іf it would be worth to also switch to a batched operation in iomap if the xarray overhead is high enough. That should be pretty trivial, but we don't really need to do it in this series.