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 79224C3404B for ; Tue, 18 Feb 2020 23:00:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 504C9207FD for ; Tue, 18 Feb 2020 23:00:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="W3IJqlJo" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727485AbgBRXAP (ORCPT ); Tue, 18 Feb 2020 18:00:15 -0500 Received: from hqnvemgate26.nvidia.com ([216.228.121.65]:5883 "EHLO hqnvemgate26.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726427AbgBRXAO (ORCPT ); Tue, 18 Feb 2020 18:00:14 -0500 Received: from hqpgpgate102.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate26.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Tue, 18 Feb 2020 14:59:59 -0800 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate102.nvidia.com (PGP Universal service); Tue, 18 Feb 2020 15:00:13 -0800 X-PGP-Universal: processed; by hqpgpgate102.nvidia.com on Tue, 18 Feb 2020 15:00:13 -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 23:00:13 +0000 Subject: Re: [PATCH v6 04/16] mm: Tweak readahead loop slightly From: John Hubbard To: Matthew Wilcox , CC: , , , , , , , , References: <20200217184613.19668-1-willy@infradead.org> <20200217184613.19668-6-willy@infradead.org> <7691abe7-d0e9-e091-b158-764fb624c2d7@nvidia.com> X-Nvconfidentiality: public Message-ID: Date: Tue, 18 Feb 2020 15:00:12 -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: <7691abe7-d0e9-e091-b158-764fb624c2d7@nvidia.com> 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=1582066800; bh=IB7kCRmqWHOCgH5gvEJMi5Ucod9FJFELOexbDWiq5WM=; h=X-PGP-Universal:Subject:From:To:CC:References:X-Nvconfidentiality: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=W3IJqlJox7bQX9XTPoXwA3Jm6LhlHKJW+mAhVNPdcUggDXvirw1BsO/uwsxWZ+7uS HOOter52f4A4hAaPodlY7f0GW7DAaw2gYdUynWMuU/ILsZ4VQHwSB4sSV1XGIKIA1A II9rNVEbC3tSkSbIrmRnLlFSPi3rJAn0dkG/YfARpEmDHSprmsPvxbe3KwU65uSj8y C3+FXfpxW4WIejSQ4+P4rtEccN3mioAXj3gOw9uQ19e5wS/+Cgx/Bb4Am7uQzPhoVD I7pTDe0JMynA0Ndr5M6yG+B/RUQjl0P9V/TbFUVySKOwDQKwJXGqsxl0tiggBN1WNv 28HLo+ojFyGyw== Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On 2/18/20 2:57 PM, John Hubbard wrote: > 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 > > Darn it, I incorrectly reviewed the N/16 patch, instead of the N/19, for this one. I thought I had deleted all those! Let me try again with the correct patch, sorry!! thanks, -- John Hubbard NVIDIA > 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, >