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 DB43BCDB482 for ; Fri, 13 Oct 2023 09:29:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230450AbjJMJ3i (ORCPT ); Fri, 13 Oct 2023 05:29:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46418 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230234AbjJMJ3g (ORCPT ); Fri, 13 Oct 2023 05:29:36 -0400 Received: from out-193.mta0.migadu.com (out-193.mta0.migadu.com [91.218.175.193]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 869C795 for ; Fri, 13 Oct 2023 02:29:33 -0700 (PDT) Message-ID: <1c91dd62-886d-bb05-8aee-22191a8a2d8e@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1697189371; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=v/wjLZqPF3Awyk9wCPsC+oeoryEbbL/rExrT85FbE7g=; b=qog+KJ+9Xz9isSq2zUiU+zGAmWX6Vo/7c67KT5LwKYrxehhgfYUCDJcSPv96fSKshioIaB MyF/YdAUO78EQywcEh7HAjhhmOEnmZm1lBjkju83Th/kt7rEwCMwqtb9sUoEb1OifPQraZ 37xNdDoUQ+XL4hpTiOW/+YWyHJFX9Xc= Date: Fri, 13 Oct 2023 17:29:19 +0800 MIME-Version: 1.0 Subject: Re: [PATCH v4 2/2] mm: Init page count in reserve_bootmem_region when MEMINIT_EARLY Content-Language: en-US To: Mike Rapoport 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 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> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yajun Deng In-Reply-To: <20231013084827.GT3303@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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, 4204K rwdata, 5608K rodata, 3188K init, 17024K bss, 5499616K reserved, 20971520K cma-reserved) after: [    0.260229] software IO TLB: area num 32. [    0.563497] Memory: 173413056K/199884452K available (18440K kernel code, 4204K rwdata, 5608K rodata, 3188K init, 17024K bss, 5499616K reserved, 20971520K cma-reserved) Memory initialization is time consuming in the boot log. > 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)) {' This is a foundation. We may change this when we are able to safely remove page init in the hotplug context one day. So the case for the early context is only temporary. >> @Mike,  By the way,  this code will cost more time: >> >>                 if (context == MEMINIT_HOTPLUG) >>                         flags = INIT_PAGE_COUNT | INIT_PAGE_RESERVED; >>                 __init_single_page(page, pfn, zone, nid, flags); >> >> >> [    0.014999] On node 0, zone DMA32: 31679 pages in unavailable ranges >> [    0.311560] ACPI: PM-Timer IO Port: 0x508 >> >> >> This code will cost less time: >> >>                 __init_single_page(page, pfn, zone, nid, 0); >>                 if (context == MEMINIT_HOTPLUG) { >>                         init_page_count(page); >>                         __SetPageReserved(page); >> >> [    0.014299] On node 0, zone DMA32: 31679 pages in unavailable ranges >> [    0.250223] ACPI: PM-Timer IO Port: 0x508 >>