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=-13.8 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 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 7341FC4361B for ; Fri, 4 Dec 2020 11:12:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3687222A85 for ; Fri, 4 Dec 2020 11:12:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387758AbgLDLMr (ORCPT ); Fri, 4 Dec 2020 06:12:47 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35216 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725839AbgLDLMr (ORCPT ); Fri, 4 Dec 2020 06:12:47 -0500 Received: from mail-pj1-x1042.google.com (mail-pj1-x1042.google.com [IPv6:2607:f8b0:4864:20::1042]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DD6EFC0613D1 for ; Fri, 4 Dec 2020 03:12:06 -0800 (PST) Received: by mail-pj1-x1042.google.com with SMTP id e5so2887683pjt.0 for ; Fri, 04 Dec 2020 03:12:06 -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=b5jT+Nn/jP36D/xoVCe9bwoBaOdsoIk7V6aoNzFbAvE=; b=BcdHi25Bn7RMXQbSWPD+ZBWFZnBRpnaIOvwShmEDBw1pmjgOAVFDuwoMj0CD4rkm0t VgKJ3IIjW1sovJBx5clrNBGHqhnRqEaLlSA/kV1XyUiggh3ZqhSjZIVWggX6dzph/JWr erQdvpszmb0Z41h9m4JuaeCb7Uqxaxn3IS2cTmzLQH4WEuzPxo08YUKIvV8aJ14+TBv1 LPGHKTGu2bnLbaMKzUokmGF/HbZL7QI3k84xBPSACOYPZoX2V3luQ8/n1vU3OKzqlt8j Gqg8El0KZhE/w2vdWygMzcsLfWGDcQ2Gjat0/ElWH1z5s3AyWkwpS8wGJAVpTKQturEi UlCw== 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=b5jT+Nn/jP36D/xoVCe9bwoBaOdsoIk7V6aoNzFbAvE=; b=ikoyXlOhdoJx6UOG8KQHvlGN+tjnA73a0/U6nBal7vWP2oqXs67Nhzmri248FX+3IZ KWF9A8DcSmWA52TLFI8wg7TSA1+cEF/uo4aaNpwB+vBg7WB3iwQ+LWBeaY3k7pHxKYfu I8bg6cM+r+NDQ3iOT1SOru479S2iIh+P7sHjoXSgg3wZ4ylHc1bSbC4VXVQSrEosmi/Y 3xJfR1yaWN1+1u2JM0FJhS4tnw8EL2E5sETgpNOMXwSuLh1b0l49bX4b0pegMCY+h7/H BgrZv0xm1G2YI9T4wleHeUCUWBZeWBKAOHE84am1uxrWkaH5LXCgiGPI+jEzYgxLgRhY 1W3Q== X-Gm-Message-State: AOAM531XMMkapi11hogHAilwH/CtPXsD5PKzvXGRtZOAlE6F/C728hx+ Bvb2D3mA/28OfbecR11z3kmlIXduaqfVmvcwsSZjdQ== X-Google-Smtp-Source: ABdhPJyyeobk+hofKbtl+NcmtLhH2L/XetFHyAPHUSkmPBkYWYiu9YEcv8h7TihQQQkqxEgO1q9iIfAFyfptA2CZYkI= X-Received: by 2002:a17:90a:ae14:: with SMTP id t20mr3740783pjq.13.1607080326455; Fri, 04 Dec 2020 03:12:06 -0800 (PST) MIME-Version: 1.0 References: <20201202121838.75218-1-songmuchun@bytedance.com> <320c8522-4ed5-809f-e6fc-8a185587519c@suse.cz> <69367ce1-eb9b-d76d-0141-da871bd826ec@suse.cz> In-Reply-To: <69367ce1-eb9b-d76d-0141-da871bd826ec@suse.cz> From: Muchun Song Date: Fri, 4 Dec 2020 19:11:30 +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 6:28 PM Vlastimil Babka wrote: > > On 12/4/20 5:03 AM, Muchun Song wrote: > > 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. > > OK, I see. > > >> > + if (max_order < MAX_ORDER && order < MAX_ORDER - 1) { > > Yes, this makes sense, as in your other patch we shouldn't check the buddy when > order == MAX_ORDER - 1 already. > > >> > /* 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; > >> > max_order++; > > OK I see now what you want to do here. the "if" may be true if we already > entered the function with order > pageblock_order. > I think we could just simplfy the "if" and "max_order++" above to: > > max_order = order + 2 > > which starts to get a bit ugly, so why not change max_order to be -1 (compared > to now) in the whole function: > > max_order = min_t(unsigned int, MAX_ORDER - 1, pageblock_order); > ... > continue_merging: > while (order < max_order) { > ... > if (order < MAX_ORDER - 1) { > // it's redundant to keep checking max_order < MAX_ORDER - 1 here after your > change, right? > ... > > max_order = order + 1; // less weird than "+ 2" > > Off by one errors, here we go! Great! Good suggestions. Thanks. > > >> 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 > > > -- Yours, Muchun