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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 82C13C34031 for ; Wed, 19 Feb 2020 01:04:37 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 42E6624655 for ; Wed, 19 Feb 2020 01:04:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 42E6624655 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=fromorbit.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id E11646B0003; Tue, 18 Feb 2020 20:04:36 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id D76BC6B0006; Tue, 18 Feb 2020 20:04:36 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C13236B0007; Tue, 18 Feb 2020 20:04:36 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0046.hostedemail.com [216.40.44.46]) by kanga.kvack.org (Postfix) with ESMTP id A23EC6B0003 for ; Tue, 18 Feb 2020 20:04:36 -0500 (EST) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 6C146180AD81A for ; Wed, 19 Feb 2020 01:04:36 +0000 (UTC) X-FDA: 76505081352.28.swim76_281ecdb447b2d X-HE-Tag: swim76_281ecdb447b2d X-Filterd-Recvd-Size: 5391 Received: from mail105.syd.optusnet.com.au (mail105.syd.optusnet.com.au [211.29.132.249]) by imf24.hostedemail.com (Postfix) with ESMTP for ; Wed, 19 Feb 2020 01:04:35 +0000 (UTC) Received: from dread.disaster.area (pa49-179-138-28.pa.nsw.optusnet.com.au [49.179.138.28]) by mail105.syd.optusnet.com.au (Postfix) with ESMTPS id 832B83A331C; Wed, 19 Feb 2020 12:04:32 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1j4Dmx-0004dF-Ul; Wed, 19 Feb 2020 12:04:31 +1100 Date: Wed, 19 Feb 2020 12:04:31 +1100 From: Dave Chinner To: Matthew Wilcox Cc: 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 v6 08/19] mm: Add readahead address space operation Message-ID: <20200219010431.GW10776@dread.disaster.area> References: <20200217184613.19668-1-willy@infradead.org> <20200217184613.19668-14-willy@infradead.org> <20200218062147.GN10776@dread.disaster.area> <20200218161004.GR7778@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200218161004.GR7778@bombadil.infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.3 cv=W5xGqiek c=1 sm=1 tr=0 a=zAxSp4fFY/GQY8/esVNjqw==:117 a=zAxSp4fFY/GQY8/esVNjqw==:17 a=jpOVt7BSZ2e4Z31A5e1TngXxSK0=:19 a=kj9zAlcOel0A:10 a=l697ptgUJYAA:10 a=JfrnYn6hAAAA:8 a=7-415B0cAAAA:8 a=J8tHrh_ofsGOLyDWh6kA:9 a=ffwTswad_GV-5CZc:21 a=o0rOaByW-dbbsVyy:21 a=CjuIK1q_8ugA:10 a=1CNFftbPRP8L7MoqJWF3:22 a=biEYGPWJfzWAr4FL6Ov7:22 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: On Tue, Feb 18, 2020 at 08:10:04AM -0800, Matthew Wilcox wrote: > On Tue, Feb 18, 2020 at 05:21:47PM +1100, Dave Chinner wrote: > > On Mon, Feb 17, 2020 at 10:45:54AM -0800, Matthew Wilcox wrote: > > > From: "Matthew Wilcox (Oracle)" > > > > > > This replaces ->readpages with a saner interface: > > > - Return void instead of an ignored error code. > > > - Pages are already in the page cache when ->readahead is called. > > > > Might read better as: > > > > - Page cache is already populates with locked pages when > > ->readahead is called. > > Will do. > > > > - Implementation looks up the pages in the page cache instead of > > > having them passed in a linked list. > > > > Add: > > > > - cleanup of unused readahead handled by ->readahead caller, not > > the method implementation. > > The readpages caller does that cleanup too, so it's not an advantage > to the readahead interface. Right. I kinda of read the list as "the reasons the new API is sane" not as "how readahead is different to readpages".... > > > ``readpages`` > > > called by the VM to read pages associated with the address_space > > > object. This is essentially just a vector version of readpage. > > > Instead of just one page, several pages are requested. > > > readpages is only used for read-ahead, so read errors are > > > ignored. If anything goes wrong, feel free to give up. > > > + This interface is deprecated; implement readahead instead. > > > > What is the removal schedule for the deprecated interface? > > I mentioned that in the cover letter; once Dave Howells has the fscache > branch merged, I'll do the remaining filesystems. Should be within the > next couple of merge windows. Sure, but I like to see actual release tags with the deprecation notice so that it's obvious to the reader as to whether this is something new and/or when they can expect it to go away. > > > +/* The byte offset into the file of this readahead block */ > > > +static inline loff_t readahead_offset(struct readahead_control *rac) > > > +{ > > > + return (loff_t)rac->_start * PAGE_SIZE; > > > +} > > > > Urk. Didn't an early page use "offset" for the page index? That > > was was "mm: Remove 'page_offset' from readahead loop" did, right? > > > > That's just going to cause confusion to have different units for > > readahead "offsets".... > > We are ... not consistent anywhere in the VM/VFS with our naming. > Unfortunately. > > $ grep -n offset mm/filemap.c > 391: * @start: offset in bytes where the range starts > ... > 815: pgoff_t offset = old->index; > ... > 2020: unsigned long offset; /* offset into pagecache page */ > ... > 2257: *ppos = ((loff_t)index << PAGE_SHIFT) + offset; > > That last one's my favourite. Not to mention the fine distinction you > and I discussed recently between offset_in_page() and page_offset(). > > Best of all, even our types encode the ambiguity of an 'offset'. We have > pgoff_t and loff_t (replacing the earlier off_t). > > So, new rule. 'pos' is the number of bytes into a file. 'index' is the > number of PAGE_SIZE pages into a file. We don't use the word 'offset' > at all. 'length' as a byte count and 'count' as a page count seem like > fine names to me. That sounds very reasonable to me. Another patchset in the making? :) Cheers, Dave. -- Dave Chinner david@fromorbit.com