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=-8.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 7F70CC3404B for ; Tue, 18 Feb 2020 22:57:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 58B2E24654 for ; Tue, 18 Feb 2020 22:57:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="MTyOyZdH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727329AbgBRW5p (ORCPT ); Tue, 18 Feb 2020 17:57:45 -0500 Received: from hqnvemgate24.nvidia.com ([216.228.121.143]:1295 "EHLO hqnvemgate24.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726427AbgBRW5o (ORCPT ); Tue, 18 Feb 2020 17:57:44 -0500 Received: from hqpgpgate102.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate24.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Tue, 18 Feb 2020 14:56:33 -0800 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate102.nvidia.com (PGP Universal service); Tue, 18 Feb 2020 14:57:43 -0800 X-PGP-Universal: processed; by hqpgpgate102.nvidia.com on Tue, 18 Feb 2020 14:57:43 -0800 Received: from [10.110.48.28] (10.124.1.5) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Tue, 18 Feb 2020 22:57:43 +0000 Subject: Re: [PATCH v6 04/16] mm: Tweak readahead loop slightly To: Matthew Wilcox , CC: , , , , , , , , References: <20200217184613.19668-1-willy@infradead.org> <20200217184613.19668-6-willy@infradead.org> X-Nvconfidentiality: public From: John Hubbard Message-ID: <7691abe7-d0e9-e091-b158-764fb624c2d7@nvidia.com> Date: Tue, 18 Feb 2020 14:57:43 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200217184613.19668-6-willy@infradead.org> X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL111.nvidia.com (172.20.187.18) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1582066593; bh=FNMoOaZBBl3i9xCcuLKNCWIelNbWmCqc+hWHl4NpXdM=; h=X-PGP-Universal:Subject:To:CC:References:X-Nvconfidentiality:From: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=MTyOyZdHZQkMODmo8rlMB/2qEg3HU5pqh9FgRxpYsmGRmONsz8OrRQrreEBM2NRJR 0PWe6O9d1zufzQnZ7Nh6PXVGWI9FIG6u5Ry+tgMofrYVgsctLaciTGIvy+/cW27I6X ozy/zXaexJDMUc/Qb0NIOSo/IRTQ4YUAKJ8AfzrVP0G+gsALpSzt/WUyZkuZM9/H1b pEHxNVaE1Zn1djE6CJLbRxf6pW4SLxI0NCI/PFJCulvIoPdYakDv8H6EHgYany/KqQ +WVDcVH0cvTLVgLvT04N+CZ78lEclF8aBvkeqi/RwbOuHLAT3Vj6DHF81hAcdWMyIY Ygo2o7pN3aTag== Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 2/17/20 10:45 AM, Matthew Wilcox wrote: > From: "Matthew Wilcox (Oracle)" > > Eliminate the page_offset variable which was just confusing; > record the start of each consecutive run of pages in the OK...presumably for the benefit of a following patch, since it is not actually consumed in this patch. > readahead_control, and move the 'kick off a fresh batch' code to > the end of the function for easier use in the next patch. That last bit was actually done in the previous patch, rather than this one, right? > > Signed-off-by: Matthew Wilcox (Oracle) > --- > mm/readahead.c | 31 +++++++++++++++++++------------ > 1 file changed, 19 insertions(+), 12 deletions(-) > > diff --git a/mm/readahead.c b/mm/readahead.c > index 15329309231f..74791b96013f 100644 > --- a/mm/readahead.c > +++ b/mm/readahead.c > @@ -154,7 +154,6 @@ void __do_page_cache_readahead(struct address_space *mapping, > unsigned long lookahead_size) > { > struct inode *inode = mapping->host; > - struct page *page; > unsigned long end_index; /* The last page we want to read */ > LIST_HEAD(page_pool); > int page_idx; > @@ -163,6 +162,7 @@ void __do_page_cache_readahead(struct address_space *mapping, > struct readahead_control rac = { > .mapping = mapping, > .file = filp, > + ._start = offset, > ._nr_pages = 0, > }; > > @@ -175,32 +175,39 @@ void __do_page_cache_readahead(struct address_space *mapping, > * Preallocate as many pages as we will need. > */ > for (page_idx = 0; page_idx < nr_to_read; page_idx++) { > - pgoff_t page_offset = offset + page_idx; You know...this ends up incrementing offset each time through the loop, so yes, the behavior is the same as when using "offset + page_idx". However, now it's a little harder to see that. IMHO the page_offset variable is not actually a bad thing, here. I'd rather keep it, all other things being equal (and I don't see any other benefits here: line count is the same, for example). What do you think? thanks, -- John Hubbard NVIDIA > + struct page *page; > > - if (page_offset > end_index) > + if (offset > end_index) > break; > > - page = xa_load(&mapping->i_pages, page_offset); > + page = xa_load(&mapping->i_pages, offset); > if (page && !xa_is_value(page)) { > /* > - * Page already present? Kick off the current batch of > - * contiguous pages before continuing with the next > - * batch. > + * Page already present? Kick off the current batch > + * of contiguous pages before continuing with the > + * next batch. This page may be the one we would > + * have intended to mark as Readahead, but we don't > + * have a stable reference to this page, and it's > + * not worth getting one just for that. > */ > - if (readahead_count(&rac)) > - read_pages(&rac, &page_pool, gfp_mask); > - rac._nr_pages = 0; > - continue; > + goto read; > } > > page = __page_cache_alloc(gfp_mask); > if (!page) > break; > - page->index = page_offset; > + page->index = offset; > list_add(&page->lru, &page_pool); > if (page_idx == nr_to_read - lookahead_size) > SetPageReadahead(page); > rac._nr_pages++; > + offset++; > + continue; > +read: > + if (readahead_count(&rac)) > + read_pages(&rac, &page_pool, gfp_mask); > + rac._nr_pages = 0; > + rac._start = ++offset; > } > > /* >