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=-13.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 C0167C4361A for ; Fri, 4 Dec 2020 04:04:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7664A222B6 for ; Fri, 4 Dec 2020 04:04:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727832AbgLDEEp (ORCPT ); Thu, 3 Dec 2020 23:04:45 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53902 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726469AbgLDEEp (ORCPT ); Thu, 3 Dec 2020 23:04:45 -0500 Received: from mail-pf1-x443.google.com (mail-pf1-x443.google.com [IPv6:2607:f8b0:4864:20::443]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2C5D9C061A4F for ; Thu, 3 Dec 2020 20:04:05 -0800 (PST) Received: by mail-pf1-x443.google.com with SMTP id q22so2781502pfk.12 for ; Thu, 03 Dec 2020 20:04:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=2eDAiT8JpRdOpG10yNUSKknpQ9yn3vAvz1tZiPhPn3k=; b=fwVknYJb6jPBmqvk6s6cfeEUQx+gsVHVu78ys5R+u0CDGq4UWVO0sUdnc1thF2NHGy RTkZJ8aqha4+ap8yz5AvnoPwVl3NJyrHwAyd8N/bSdyuJikCfmwf+SgSywJ7VP0MOyH1 IG+lSErohD9I2fTblNKKlBRf0PlUB3R9AVdSxwmNdGSYyZWSnwQxQcUiuC3CHZ8TwLpp C2pTyCNfC4nQQ5yDFUeJQpacZnf/iU63wGNKT/7aXtTw3FWaRLcnTI3haf7rsbQTIXo3 USQZiYC5ogIhBcYGwEJJAdq4ahonSkjTzgpuWGo1egHCZ4eXoXlUuTXbCeXFRiktCWUy Vb+g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=2eDAiT8JpRdOpG10yNUSKknpQ9yn3vAvz1tZiPhPn3k=; b=URFHChWPneigy9Vz3aBDrtVulfnNf/MxE2eWpJJLh+UqKWE+WhOTQ5SfRvnuuXOBmL Eu5WSCZNvhpuaZBd8QdxNq0K1Upkzv5eglBPj27rD4pw1xDbXDhrltbIUMFjk/JRmdAC iHj7yEnOzqAvo/x9jmnolBL+f31Cpsy1yJiVxnS/q80iVXN7vARoBojMd1ULCM0ajYjS oqe1UWznl7cYBijcA/5didnThf/85CWtznb8ae7QQmgdECqDwK0sYcVR0pHTPH1HGJjZ tGgkiSK31luluSeLTBzjy1Zb0NsFYmmOs20hPVU+KeYHl2012Uqyz3eQVwTI+7RSdHvg uq3g== X-Gm-Message-State: AOAM533cr2cAODYBMMYWJW4aicjVNPruOFZql6Fzj77Prqd3HEQZJxX+ /HidjVuZ5bHr4hBwILMys9+8DRrWRSJi55XOAj0TOw== X-Google-Smtp-Source: ABdhPJyhRx3B/Sl+EWbtdAIQ7o9hmGRtatp3AEm01dQvzs1sJ2EfeJQpUqP1ABanFUAqEehdsORysmAoAGm3k5yrb+8= X-Received: by 2002:aa7:8105:0:b029:18e:c8d9:2c24 with SMTP id b5-20020aa781050000b029018ec8d92c24mr1992887pfi.49.1607054644672; Thu, 03 Dec 2020 20:04:04 -0800 (PST) MIME-Version: 1.0 References: <20201202121838.75218-1-songmuchun@bytedance.com> <320c8522-4ed5-809f-e6fc-8a185587519c@suse.cz> In-Reply-To: <320c8522-4ed5-809f-e6fc-8a185587519c@suse.cz> From: Muchun Song Date: Fri, 4 Dec 2020 12:03:28 +0800 Message-ID: Subject: Re: [External] Re: [PATCH] mm/page_alloc: speeding up the iteration of max_order To: Vlastimil Babka Cc: Andrew Morton , Linux Memory Management List , LKML Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 4, 2020 at 1:37 AM Vlastimil Babka wrote: > > On 12/2/20 1:18 PM, Muchun Song wrote: > > When we free a page whose order is very close to MAX_ORDER and greater > > than pageblock_order, it wastes some CPU cycles to increase max_order > > to MAX_ORDER one by one and check the pageblock migratetype of that page > > But we have to do that. It's not the same page, it's the merged page and the new > buddy is a different pageblock and we need to check if they have compatible > migratetypes and can merge, or we have to bail out. So the patch is wrong. > > > repeatedly especially when MAX_ORDER is much larger than pageblock_order. > > Do we have such architectures/configurations anyway? > > > Signed-off-by: Muchun Song > > --- > > mm/page_alloc.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 141f12e5142c..959541234e1d 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -1041,7 +1041,7 @@ static inline void __free_one_page(struct page *page, > > pfn = combined_pfn; > > order++; > > } > > - if (max_order < MAX_ORDER) { If we free a page with order == MAX_ORDER - 1, it has no buddy. The following pageblock operation is also pointless. > > + if (max_order < MAX_ORDER && order < MAX_ORDER - 1) { > > /* If we are here, it means order is >= pageblock_order. > > * We want to prevent merge between freepages on isolate > > * pageblock and normal pageblock. Without this, pageblock > > @@ -1062,6 +1062,8 @@ static inline void __free_one_page(struct page *page, > > is_migrate_isolate(buddy_mt))) > > goto done_merging; > > } > > + if (unlikely(order != max_order - 1)) > > + max_order = order + 1; > > Or maybe I just don't understand what this is doing. When is the new 'if' even > true? We just bailed out of "while (order < max_order - 1)" after the last > "order++", which means it should hold that "order == max_order - 1")? No, I do not agree. The MAX_ORDER may be greater than 11. # git grep "CONFIG_FORCE_MAX_ZONEORDER" # arch/arm/configs/imx_v6_v7_defconfig:CONFIG_FORCE_MAX_ZONEORDER=14 # arch/powerpc/configs/85xx/ge_imp3a_defconfig:CONFIG_FORCE_MAX_ZONEORDER=17 # arch/powerpc/configs/fsl-emb-nonhw.config:CONFIG_FORCE_MAX_ZONEORDER=13 Have you seen it? On some architecture, the MAX_ORDER can be 17. When we free a page with an order 16. Without this patch, the max_order should be increased one by one from 10 to 17. Thanks. > Your description sounds like you want to increase max_order to MAX_ORDER in one > step, which as I explained would be wrong. But the implementation looks actually > like a no-op. > > > max_order++; > > goto continue_merging; > > } > > > -- Yours, Muchun