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 CEDB3CDB483 for ; Mon, 16 Oct 2023 08:10:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231861AbjJPIKt (ORCPT ); Mon, 16 Oct 2023 04:10:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55014 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231149AbjJPIKp (ORCPT ); Mon, 16 Oct 2023 04:10:45 -0400 Received: from out-208.mta1.migadu.com (out-208.mta1.migadu.com [IPv6:2001:41d0:203:375::d0]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B2245B4 for ; Mon, 16 Oct 2023 01:10:42 -0700 (PDT) Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1697443840; 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=Ftz3kg8fbbtLXGwBLfTxu3Gnc6ZKz1jBxA85bC9wrOk=; b=nnR1GG0xec5M/KvAHK28cBptgNPCmVGOaZjqotTcoVDzPs80vU8ciWHo/TiVLDz7x74rF9 cJLTrH2lARxwGUIkiSLvuS9AbZ5+yKLJ3LoWPu+cvyBMXBW1uDllFBFIZ8ddSn0U0GQ6IW TxWJp5fT9c+O1BPNTmY6OVv7uTy/oZQ= Date: Mon, 16 Oct 2023 16:10:30 +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> <1c91dd62-886d-bb05-8aee-22191a8a2d8e@linux.dev> <20231016063357.GU3303@kernel.org> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yajun Deng In-Reply-To: <20231016063357.GU3303@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 2023/10/16 14:33, Mike Rapoport wrote: > 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: >> 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? before: [   10.692708] Run /init as init process after: [   10.666290] Run /init as init process About 0.25%. The total boot time is variable, depending on how many drivers need to be initialized. > >>> 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. To avoid introducing MEMINIT_LATE context and make code simpler. This might be a better option. if (page_count(page) || PageReserved(page))