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 6D6F5C1975A for ; Wed, 25 Mar 2020 15:32:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4468C206F8 for ; Wed, 25 Mar 2020 15:32:35 +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="nwr8fvcC" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727707AbgCYPcb (ORCPT ); Wed, 25 Mar 2020 11:32:31 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:53644 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727491AbgCYPca (ORCPT ); Wed, 25 Mar 2020 11:32:30 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=L8UzQwxATOZdjWZ+3tNM04b2mH/5tj4IRSDfIFAnCq4=; b=nwr8fvcCAKrcOHuwe8r/p16lMc bZh3DEdAU9aGBWN3F5ynv1Ne93Ij03ZhftdP2p/j/SwKFdDbTLj5/ZaltpVeKwhDVOtZpmt6dBgOM Y5kNAkTDyJM9LmxIOgZivD4BtHVK41PC4z2UtEwA8qUzMYjVHQwzjfESuvsJdyTL91AdLqA/lHmDm b4ONx8n6tUgKbzMesC9PHNx/tJe345Szba01BQVbNkeQ4aBKyS9/rqkTgJMFlzt5JsbGeTzjBPG19 tW79XBGQHh8i08Okr8byBxVFG1QH7u5q9rAcay5PaTaRDoWupoIchhUNkRzhk4f/AQVLTP2rNvR7K 5pnTChzQ==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jH816-0004oZ-U3; Wed, 25 Mar 2020 15:32:28 +0000 Date: Wed, 25 Mar 2020 08:32:28 -0700 From: Matthew Wilcox To: Miklos Szeredi Cc: Andrew Morton , 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 , Dave Chinner , William Kucharski Subject: Re: [PATCH v10 24/25] fuse: Convert from readpages to readahead Message-ID: <20200325153228.GB22483@bombadil.infradead.org> References: <20200323202259.13363-1-willy@infradead.org> <20200323202259.13363-25-willy@infradead.org> <20200325120254.GA22483@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Wed, Mar 25, 2020 at 03:43:02PM +0100, Miklos Szeredi wrote: > > > > - while ((page = readahead_page(rac))) { > > - if (fuse_readpages_fill(&data, page) != 0) > > + nr_pages = min(readahead_count(rac), fc->max_pages); > > Missing fc->max_read clamp. Yeah, I realised that. I ended up doing ... + unsigned int i, max_pages, nr_pages = 0; ... + max_pages = min(fc->max_pages, fc->max_read / PAGE_SIZE); > > + ia = fuse_io_alloc(NULL, nr_pages); > > + if (!ia) > > return; > > + ap = &ia->ap; > > + __readahead_batch(rac, ap->pages, nr_pages); > > nr_pages = __readahead_batch(...)? That's the other bug ... this was designed for btrfs which has a fixed-size buffer. But you want to dynamically allocate fuse_io_args(), so we need to figure out the number of pages beforehand, which is a little awkward. I've settled on this for the moment: for (;;) { struct fuse_io_args *ia; struct fuse_args_pages *ap; nr_pages = readahead_count(rac) - nr_pages; if (nr_pages > max_pages) nr_pages = max_pages; if (nr_pages == 0) break; ia = fuse_io_alloc(NULL, nr_pages); if (!ia) return; ap = &ia->ap; __readahead_batch(rac, ap->pages, nr_pages); for (i = 0; i < nr_pages; i++) { fuse_wait_on_page_writeback(inode, readahead_index(rac) + i); ap->descs[i].length = PAGE_SIZE; } ap->num_pages = nr_pages; fuse_send_readpages(ia, rac->file); } but I'm not entirely happy with that either. Pondering better options. > This will give consecutive pages, right? readpages() was already being called with consecutive pages. Several filesystems had code to cope with the pages being non-consecutive, but that wasn't how the core code worked; if there was a discontiguity it would send off the pages that were consecutive and start a new batch. __readahead_batch() can't return fewer than nr_pages, so you don't need to check for that.