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 DD14FC34045 for ; Tue, 18 Feb 2020 15:42:37 +0000 (UTC) Received: from lists.sourceforge.net (lists.sourceforge.net [216.105.38.7]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id AE17622527; Tue, 18 Feb 2020 15:42:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=sourceforge.net header.i=@sourceforge.net header.b="ibnGNIuF"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=sf.net header.i=@sf.net header.b="ln+xbSH0"; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Wj2hN1Ys" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AE17622527 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linux-f2fs-devel-bounces@lists.sourceforge.net Received: from [127.0.0.1] (helo=sfs-ml-1.v29.lw.sourceforge.com) by sfs-ml-1.v29.lw.sourceforge.com with esmtp (Exim 4.90_1) (envelope-from ) id 1j451A-0008ME-UD; Tue, 18 Feb 2020 15:42:36 +0000 Received: from [172.30.20.202] (helo=mx.sourceforge.net) by sfs-ml-1.v29.lw.sourceforge.com with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1j4519-0008Lo-AH for linux-f2fs-devel@lists.sourceforge.net; Tue, 18 Feb 2020 15:42:35 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sourceforge.net; s=x; 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:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=oQ+wHGdx1ULBXPBam1g8Uipf1yyfaaqxmlrcZ982o9k=; b=ibnGNIuFdcBS4P9FrUhV1+6xyN Rtd9A1nsc9XAtqaDxl+KfcDNLv8OHs3uezOKmiNngZvzYLtr+s3YFoX1U0QvIghlr9WI10b9RG4gG yLvf/D3bMvoo+sIYiF9qfVIJhJU44/Kg8ajtd9SqlW0n7hq8HImkv7lRsTGqVtf1EVAQ=; DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sf.net; s=x ; 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:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=oQ+wHGdx1ULBXPBam1g8Uipf1yyfaaqxmlrcZ982o9k=; b=ln+xbSH0N/zO4DQH1bzGRYerqq eKIVoo/u8fnPUyok/BRajwD9T4VcBDGtJTSpnXeHN2R3l4uKJG2t9yVwIvxqhAOy6w2AB3o32iKsK Wh3A9bObQ3II4tfgcFWMTtaDIfCCtu5a/Eg54ekTCY+uX5pwU5ESMhhw7EGHEvPci+MQ=; Received: from bombadil.infradead.org ([198.137.202.133]) by sfi-mx-4.v28.lw.sourceforge.com with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.92.2) id 1j4517-0076mQ-Lu for linux-f2fs-devel@lists.sourceforge.net; Tue, 18 Feb 2020 15:42:35 +0000 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=oQ+wHGdx1ULBXPBam1g8Uipf1yyfaaqxmlrcZ982o9k=; b=Wj2hN1Ys6lneGYnt6lyt28p7dX xcPHY3DggtQF0V8rHudxsyMEruSBB+yksYd5K4jTPpH1Sb6FwieHFjL9L4y2tE2u/FKfJKGHM07zk 7aVuKRme2EL4Yz9RAVR+an3Misj05c3UKPtIB2h8TZRI5Is3OFhiQdPCfewKzO/jjjB0pr4J84clk JoeAVeGLWbHKY/xgLceP9WBHTLk19SxEnQx8FM7lcnxbWFWqoM7F8w+JhQvm0Ci7daJwE+nGYHtn3 +8vcZGb7YOcxncpzTgWcLFEqCwt6gz/YgXx5oaJ9EhecdpELGPuj8YQkK5ZbDKGuAWwReHfNZzohN EfWd+hMA==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j450w-0007Ik-FJ; Tue, 18 Feb 2020 15:42:22 +0000 Date: Tue, 18 Feb 2020 07:42:22 -0800 From: Matthew Wilcox To: Dave Chinner Message-ID: <20200218154222.GQ7778@bombadil.infradead.org> References: <20200217184613.19668-1-willy@infradead.org> <20200217184613.19668-12-willy@infradead.org> <20200218061459.GM10776@dread.disaster.area> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200218061459.GM10776@dread.disaster.area> X-Headers-End: 1j4517-0076mQ-Lu Subject: Re: [f2fs-dev] [PATCH v6 07/19] mm: Put readahead pages in cache earlier X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com, linux-mm@kvack.org, ocfs2-devel@oss.oracle.com, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-btrfs@vger.kernel.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net On Tue, Feb 18, 2020 at 05:14:59PM +1100, Dave Chinner wrote: > On Mon, Feb 17, 2020 at 10:45:52AM -0800, Matthew Wilcox wrote: > > From: "Matthew Wilcox (Oracle)" > > > > At allocation time, put the pages in the cache unless we're using > > ->readpages. Add the readahead_for_each() iterator for the benefit of > > the ->readpage fallback. This iterator supports huge pages, even though > > none of the filesystems to be converted do yet. > > This could be better written - took me some time to get my head > around it and the code. > > "When populating the page cache for readahead, mappings that don't > use ->readpages need to have their pages added to the page cache > before ->readpage is called. Do this insertion earlier so that the > pages can be looked up immediately prior to ->readpage calls rather > than passing them on a linked list. This early insert functionality > is also required by the upcoming ->readahead method that will > replace ->readpages. > > Optimise and simplify the readpage loop by adding a > readahead_for_each() iterator to provide the pages we need to read. > This iterator also supports huge pages, even though none of the > filesystems have been converted to use them yet." Thanks, I'll use that. > > +static inline struct page *readahead_page(struct readahead_control *rac) > > +{ > > + struct page *page; > > + > > + if (!rac->_nr_pages) > > + return NULL; > > Hmmmm. > > > + > > + page = xa_load(&rac->mapping->i_pages, rac->_start); > > + VM_BUG_ON_PAGE(!PageLocked(page), page); > > + rac->_batch_count = hpage_nr_pages(page); > > So we could have rac->_nr_pages = 2, and then we get an order 2 > large page returned, and so rac->_batch_count = 4. Well, no, we couldn't. rac->_nr_pages is incremented by 4 when we add an order-2 page to the readahead. I can put a BUG_ON(rac->_batch_count > rac->_nr_pages) in here to be sure to catch any logic error like that. > > @@ -159,6 +152,7 @@ void __do_page_cache_readahead(struct address_space *mapping, > > unsigned long i; > > loff_t isize = i_size_read(inode); > > gfp_t gfp_mask = readahead_gfp_mask(mapping); > > + bool use_list = mapping->a_ops->readpages; > > struct readahead_control rac = { > > .mapping = mapping, > > .file = filp, > > [ I do find these unstructured mixes of declarations and > initialisations dense and difficult to read.... ] Fair ... although I didn't create this mess, I can tidy it up a bit. > > - page->index = offset; > > - list_add(&page->lru, &page_pool); > > + if (use_list) { > > + page->index = offset; > > + list_add(&page->lru, &page_pool); > > + } else if (add_to_page_cache_lru(page, mapping, offset, > > + gfp_mask) < 0) { > > + put_page(page); > > + goto read; > > + } > > Ok, so that's why you put read code at the end of the loop. To turn > the code into spaghetti :/ > > How much does this simplify down when we get rid of ->readpages and > can restructure the loop? This really seems like you're trying to > flatten two nested loops into one by the use of goto.... I see it as having two failure cases in this loop. One for "page is already present" (which already existed) and one for "allocated a page, but failed to add it to the page cache" (which used to be done later). I didn't want to duplicate the "call read_pages()" code. So I reshuffled the code rather than add a nested loop. I don't think the nested loop is easier to read (we'll be at 5 levels of indentation for some statements). Could do it this way ... @@ -218,18 +218,17 @@ void page_cache_readahead_limit(struct address_space *mapping, } else if (add_to_page_cache_lru(page, mapping, offset, gfp_mask) < 0) { put_page(page); - goto read; +read: + if (readahead_count(&rac)) + read_pages(&rac, &page_pool); + rac._nr_pages = 0; + rac._start = ++offset; + continue; } if (i == nr_to_read - lookahead_size) SetPageReadahead(page); rac._nr_pages++; offset++; - continue; -read: - if (readahead_count(&rac)) - read_pages(&rac, &page_pool); - rac._nr_pages = 0; - rac._start = ++offset; } /* but I'm not sure that's any better. _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel