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 DB554E7849A for ; Mon, 2 Oct 2023 08:59:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235976AbjJBI71 (ORCPT ); Mon, 2 Oct 2023 04:59:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32820 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235961AbjJBI7V (ORCPT ); Mon, 2 Oct 2023 04:59:21 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 01AE23C31 for ; Mon, 2 Oct 2023 01:56:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1696237015; 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=kZolH99067fvKHUQAUHeclQlPt0YjXr+P4dEn1LOWbQ=; b=CXvEsq9VSlASyzVd5KOmW1Bv4g1dE+A8WMIRiyLn0evRBQ66sz71RYQ+xTBPJfsFTSatHZ B6RzrNx7/XxLUzP1TqU1PPSbr00aHo51DIeBg/JhHtI3Qkr7LYtXa493fEDL2fAUcJ+Alq +vbec04xtvHN0vFwL5vg60kLd8bu8wg= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-14-zxibARMDMNSbqEtobKKvtg-1; Mon, 02 Oct 2023 04:56:54 -0400 X-MC-Unique: zxibARMDMNSbqEtobKKvtg-1 Received: by mail-wr1-f69.google.com with SMTP id ffacd0b85a97d-30e3ee8a42eso12027773f8f.1 for ; Mon, 02 Oct 2023 01:56:54 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1696237013; x=1696841813; h=content-transfer-encoding:in-reply-to:organization:from:references :cc:to:content-language:subject:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=kZolH99067fvKHUQAUHeclQlPt0YjXr+P4dEn1LOWbQ=; b=Epl2AMHD825SJjjoG0o7xWjmpelrEk5DnOzn+34NxijLoxDyF3FjAPvi4jYIglR/kX 3FHDF/F3zMyLxXKWJPYtcUWHWqDymo3MBkvDLztPbRy/96/bh5YHzLw8MroqYUQxTCWf eq99JIGPiQqqzqmfctetNfx46Fg77ZJ2B0U8RdhhyDnoQVsYyeLtz8lMwGedzfR11x2R a2jY42zhyVZ3evdI6gMhx9oi3TuXHgPnprtKaqZCZ6L7wFVdDI2hHzSWi3zO+DvvN3KR ziOhMp6JWBbveXBdu/iSWrHPjRpnc5KQ6GEjzd0kTpg1tSjpisQqjsRl/boeSvpZWjR5 LVUg== X-Gm-Message-State: AOJu0YzMqre9JMxeb9nLMtlDufpZhEq5QazuqbV+ySVUlMry0btD/IUx dgwbTXWF+Tcl4J493P3XG3A0O/RTmD+qBZhE8mGmaXXz1cSR61jw8S94H5wI65GcuD/969BR/+y a62FBsYKALh/HL0cFf4vurXPL X-Received: by 2002:a5d:668a:0:b0:321:5969:d465 with SMTP id l10-20020a5d668a000000b003215969d465mr9091194wru.65.1696237013400; Mon, 02 Oct 2023 01:56:53 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFNivYmW4PtO+ePKJDFQz9ZH3hXp+F3LiyWwZ9zsgVXl2tVW95sg/9viMCcYxcA7zlnFJjn2Q== X-Received: by 2002:a5d:668a:0:b0:321:5969:d465 with SMTP id l10-20020a5d668a000000b003215969d465mr9091177wru.65.1696237012975; Mon, 02 Oct 2023 01:56:52 -0700 (PDT) Received: from ?IPV6:2003:cb:c735:f200:cb49:cb8f:88fc:9446? (p200300cbc735f200cb49cb8f88fc9446.dip0.t-ipconnect.de. [2003:cb:c735:f200:cb49:cb8f:88fc:9446]) by smtp.gmail.com with ESMTPSA id 11-20020a056000156b00b0032485046055sm9783325wrz.5.2023.10.02.01.56.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Oct 2023 01:56:52 -0700 (PDT) Message-ID: Date: Mon, 2 Oct 2023 10:56:51 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [PATCH v4 2/2] mm: Init page count in reserve_bootmem_region when MEMINIT_EARLY Content-Language: en-US To: Mike Rapoport , Yajun Deng Cc: 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> <20230929100252.GW3303@kernel.org> <15233624-f32e-172e-b2f6-7ca7bffbc96d@linux.dev> <20231001185934.GX3303@kernel.org> <90342474-432a-9fe3-2f11-915a04f0053f@linux.dev> <20231002084708.GZ3303@kernel.org> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20231002084708.GZ3303@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02.10.23 10:47, Mike Rapoport wrote: > On Mon, Oct 02, 2023 at 03:03:56PM +0800, Yajun Deng wrote: >> >> On 2023/10/2 02:59, Mike Rapoport wrote: >>> On Fri, Sep 29, 2023 at 06:27:25PM +0800, Yajun Deng wrote: >>>> On 2023/9/29 18:02, Mike Rapoport wrote: >>>>>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>>>>>>> index 06be8821d833..b868caabe8dc 100644 >>>>>>>> --- a/mm/page_alloc.c >>>>>>>> +++ b/mm/page_alloc.c >>>>>>>> @@ -1285,18 +1285,22 @@ void __free_pages_core(struct page *page, unsigned int order) >>>>>>>> unsigned int loop; >>>>>>>> /* >>>>>>>> - * When initializing the memmap, __init_single_page() sets the refcount >>>>>>>> - * of all pages to 1 ("allocated"/"not free"). We have to set the >>>>>>>> - * refcount of all involved pages to 0. >>>>>>>> + * When initializing the memmap, memmap_init_range sets the refcount >>>>>>>> + * of all pages to 1 ("reserved" and "free") in hotplug context. We >>>>>>>> + * have to set the refcount of all involved pages to 0. Otherwise, >>>>>>>> + * we don't do it, as reserve_bootmem_region only set the refcount on >>>>>>>> + * reserve region ("reserved") in early context. >>>>>>>> */ >>>>>>> Again, why hotplug and early init should be different? >>>>>> I will add a comment that describes it will save boot time. >>>>> But why do we need initialize struct pages differently at boot time vs >>>>> memory hotplug? >>>>> Is there a reason memory hotplug cannot have page count set to 0 just like >>>>> for pages reserved at boot time? >>>> This patch just save boot time in MEMINIT_EARLY. If someone finds out that >>>> it can save time in >>>> >>>> MEMINIT_HOTPLUG, I think it can be done in another patch later. I just >>>> keeping it in the same. >>> But it's not the same. It becomes slower after your patch and the code that >>> frees the pages for MEMINIT_EARLY and MEMINIT_HOTPLUG becomes non-uniform >>> for no apparent reason. >> >> __free_pages_core will also be called by others, such as: >> deferred_free_range, do_collection and memblock_free_late. >> >> We couldn't remove  'if (page_count(page))' even if we set page count to 0 >> when MEMINIT_HOTPLUG. > > That 'if' breaks the invariant that __free_pages_core is always called for > pages with initialized page count. Adding it may lead to subtle bugs and > random memory corruption so we don't want to add it at the first place. As long as we have to special-case memory hotplug, we know that we are always coming via generic_online_page() in that case. We could either move some logic over there, or let __free_pages_core() know what it should do. -- Cheers, David / dhildenb