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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CEED4CDB465 for ; Mon, 16 Oct 2023 06:35:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231801AbjJPGfG (ORCPT ); Mon, 16 Oct 2023 02:35:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52270 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229831AbjJPGfE (ORCPT ); Mon, 16 Oct 2023 02:35:04 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1AA4DA2 for ; Sun, 15 Oct 2023 23:35:03 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C9292C433C9; Mon, 16 Oct 2023 06:34:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1697438102; bh=h7+mxeWvHopjpfHs2M8yjcff71cFlFkVRyP3Nk6y5ug=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=jstQ79TMlhwJYum7iRHmZ3sYsFdhRBmZNHatoTTONDq4i2VQqXW4b1vYrdUg/4W4D tlcZBRLmwsoxhCxp2qZ1j72B+TV1FNXpWTD05OpkfF4MNLn1I3OjkCatEbRfabkrdw xmSZi6ogdkNHGS/Qoiahu87CmPpHSDzkUNceJ1o3/NlM2gpdleDNJrUK73R+snwRKt 37IBhXMSnmeXRRg+FfbxX5WojUbiHSneflTGBGzRToWbiQ2Qsr07mGm9CQMau4f7RK 16wgGzy6tVlgGlc6D3sxIERes1x6pjk9mh9x6XwGZLEMggjmILqnLoXBLsgbvC11f6 cr4DtyhYP+exA== Date: Mon, 16 Oct 2023 09:33:57 +0300 From: Mike Rapoport To: Yajun Deng Cc: David Hildenbrand , akpm@linux-foundation.org, mike.kravetz@oracle.com, muchun.song@linux.dev, willy@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 2/2] mm: Init page count in reserve_bootmem_region when MEMINIT_EARLY Message-ID: <20231016063357.GU3303@kernel.org> References: <20230928083302.386202-1-yajun.deng@linux.dev> <20230928083302.386202-3-yajun.deng@linux.dev> <20230929083018.GU3303@kernel.org> <2f8c4741-5c7f-272d-9cef-9fda9fbc7ca6@linux.dev> <5382bf2d-5aa0-1498-8169-3248be4b5af3@linux.dev> <38cd0cb9-efe9-b98a-2768-ccb48da8b812@linux.dev> <20231013084827.GT3303@kernel.org> <1c91dd62-886d-bb05-8aee-22191a8a2d8e@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1c91dd62-886d-bb05-8aee-22191a8a2d8e@linux.dev> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 13, 2023 at 05:29:19PM +0800, Yajun Deng wrote: > > On 2023/10/13 16:48, Mike Rapoport wrote: > > On Thu, Oct 12, 2023 at 05:53:22PM +0800, Yajun Deng wrote: > > > On 2023/10/12 17:23, David Hildenbrand wrote: > > > > On 10.10.23 04:31, Yajun Deng wrote: > > > > > On 2023/10/8 16:57, Yajun Deng wrote: > > > > > > > That looks wrong. if the page count would by pure luck be 0 > > > > > > > already for hotplugged memory, you wouldn't clear the reserved > > > > > > > flag. > > > > > > > > > > > > > > These changes make me a bit nervous. > > > > > > Is 'if (page_count(page) || PageReserved(page))' be safer? Or do I > > > > > > need to do something else? > > > > > > > > > > > How about the following if statement? But it needs to add more patch > > > > > like v1 ([PATCH 2/4] mm: Introduce MEMINIT_LATE context). > > > > > > > > > > It'll be safer, but more complex. Please comment... > > > > > > > > > >     if (context != MEMINIT_EARLY || (page_count(page) || > > > > > PageReserved(page)) { > > > > > > > > > Ideally we could make initialization only depend on the context, and not > > > > check for count or the reserved flag. > > > > > > > This link is v1, > > > https://lore.kernel.org/all/20230922070923.355656-1-yajun.deng@linux.dev/ > > > > > > If we could make initialization only depend on the context, I'll modify it > > > based on v1. > > Although ~20% improvement looks impressive, this is only optimization of a > > fraction of the boot time, and realistically, how much 56 msec saves from > > the total boot time when you boot a machine with 190G of RAM? > > There are a lot of factors that can affect the total boot time. 56 msec > saves may be insignificant. > > But if we look at the boot log, we'll see there's a significant time jump. > > before: > > [    0.250334] ACPI: PM-Timer IO Port: 0x508 > [    0.618994] Memory: 173413056K/199884452K available (18440K kernel code, > > after: > > [    0.260229] software IO TLB: area num 32. > [    0.563497] Memory: 173413056K/199884452K available (18440K kernel code, > > Memory initialization is time consuming in the boot log. You just confirmed that 56 msec is insignificant and then you send again the improvement of ~60 msec in memory initialization. What does this improvement gain in percentage of total boot time? > > I still think the improvement does not justify the churn, added complexity > > and special casing of different code paths of initialization of struct pages. > > > Because there is a loop, if the order is MAX_ORDER, the loop will run 1024 > times. The following 'if' would be safer: > > 'if (context != MEMINIT_EARLY || (page_count(page) || >> PageReserved(page)) > {' No, it will not. As the matter of fact any condition here won't be 'safer' because it makes the code more complex and less maintainable. Any future change in __free_pages_core() or one of it's callers will have to reason what will happen with that condition after the change. -- Sincerely yours, Mike.