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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 A1B3DC2D0E4 for ; Mon, 23 Nov 2020 10:37:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4609B207FF for ; Mon, 23 Nov 2020 10:37:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=bytedance-com.20150623.gappssmtp.com header.i=@bytedance-com.20150623.gappssmtp.com header.b="UTFKQgOo" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728291AbgKWKhP (ORCPT ); Mon, 23 Nov 2020 05:37:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38310 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726325AbgKWKhP (ORCPT ); Mon, 23 Nov 2020 05:37:15 -0500 Received: from mail-pg1-x541.google.com (mail-pg1-x541.google.com [IPv6:2607:f8b0:4864:20::541]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AC830C061A4E for ; Mon, 23 Nov 2020 02:37:13 -0800 (PST) Received: by mail-pg1-x541.google.com with SMTP id f17so5340602pge.6 for ; Mon, 23 Nov 2020 02:37:13 -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=4eFIlDBCGuePrKXo7ssxRUnh/an23uWR8hRv/nfBrew=; b=UTFKQgOoJYizpumITmdB9VlaPcXqQMrksxuklKmUZv6ApbQDov2zF5scuZArYl6A6Y yd++i3f42p9lH3up/PA2WaDRuPwQVAlAVGj44ZMj/p0UxW8aMb/UDXzHAF/8F7bjBa92 bNWPUY6R2T4umft7PJYwJOFOPTOsAdzFQfZAkD+cIEIIb//UmiUZGZ33v4AVzaZhwBTj td+K9uJO9oe3itDjbfRgjBVVceT1Wxzx39v5xAZ9+5rFZiJf0ZCiTgQdV7Do5bTaS6It MOItu/J02q00pSJgoJsVqQaJlPL3pCB/UEdDyK5E5dY97QGYQUJWZ/U/NsRTqHV7m9pk Gz8g== 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=4eFIlDBCGuePrKXo7ssxRUnh/an23uWR8hRv/nfBrew=; b=c3ST7T1weZjh+vu4wHOHUdEtiXTaRoTqmZVfaO/gouG055Yikjm4Qta3X1DktFQqup MapPjxhQE+4o/FUFEhZFbftPepjZxJyhBSzlbXWIUTZVIBGNj3NVGf1DDLVXYcQlYv8n yz/CIKkAS5rDczJrOVHx50wde+PjG2kCAVdpHvYnFpz2tj2Qp9OAgf/ocPrVFGNbK+f+ eDQsGpMFcNnGgWixAz4giPOlAVrUPrB4G2JrVr3qE1f8I8pPVPUv4ykufoQlA5bgZ5pL is/gAb5Ufxf0Cst0cJh5nyGWViZD5mrIrJOaWSBytovcbqeOHJGpCSBAvFiWsID5gd8a 9Nsg== X-Gm-Message-State: AOAM5323EHzR+sPVi92J2tzs7mpGu4qsgnGmKXG4J2SPZUXsqZUT+sEJ AtuB/tYGuD0ts8MQzdq6dqCuKwaAYJrrEy215sGSuQ== X-Google-Smtp-Source: ABdhPJz8PxEYWSwkBesY8S8Gp7xJgr4OI3mDgYlO5QJdSzdxdF6WwhS7tyxFNc2WD1b+YhcyppNVwief6iy0SpHqQSI= X-Received: by 2002:a63:fe0c:: with SMTP id p12mr26221772pgh.31.1606127833192; Mon, 23 Nov 2020 02:37:13 -0800 (PST) MIME-Version: 1.0 References: <20201120064325.34492-1-songmuchun@bytedance.com> <20201120084202.GJ3200@dhcp22.suse.cz> <20201120131129.GO3200@dhcp22.suse.cz> <20201123074046.GB27488@dhcp22.suse.cz> <20201123094344.GG27488@dhcp22.suse.cz> In-Reply-To: <20201123094344.GG27488@dhcp22.suse.cz> From: Muchun Song Date: Mon, 23 Nov 2020 18:36:33 +0800 Message-ID: Subject: Re: [External] Re: [PATCH v5 00/21] Free some vmemmap pages of hugetlb page To: Michal Hocko Cc: Jonathan Corbet , Mike Kravetz , Thomas Gleixner , mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, Peter Zijlstra , viro@zeniv.linux.org.uk, Andrew Morton , paulmck@kernel.org, mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com, Randy Dunlap , oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, Mina Almasry , David Rientjes , Matthew Wilcox , Oscar Salvador , "Song Bao Hua (Barry Song)" , Xiongchun duan , linux-doc@vger.kernel.org, LKML , Linux Memory Management List , linux-fsdevel Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 23, 2020 at 5:43 PM Michal Hocko wrote: > > On Mon 23-11-20 16:53:53, Muchun Song wrote: > > On Mon, Nov 23, 2020 at 3:40 PM Michal Hocko wrote: > > > > > > On Fri 20-11-20 23:44:26, Muchun Song wrote: > > > > On Fri, Nov 20, 2020 at 9:11 PM Michal Hocko wrote: > > > > > > > > > > On Fri 20-11-20 20:40:46, Muchun Song wrote: > > > > > > On Fri, Nov 20, 2020 at 4:42 PM Michal Hocko wrote: > > > > > > > > > > > > > > On Fri 20-11-20 14:43:04, Muchun Song wrote: > > > > > > > [...] > > > > > > > > > > > > > > Thanks for improving the cover letter and providing some numbers. I have > > > > > > > only glanced through the patchset because I didn't really have more time > > > > > > > to dive depply into them. > > > > > > > > > > > > > > Overall it looks promissing. To summarize. I would prefer to not have > > > > > > > the feature enablement controlled by compile time option and the kernel > > > > > > > command line option should be opt-in. I also do not like that freeing > > > > > > > the pool can trigger the oom killer or even shut the system down if no > > > > > > > oom victim is eligible. > > > > > > > > > > > > Hi Michal, > > > > > > > > > > > > I have replied to you about those questions on the other mail thread. > > > > > > > > > > > > Thanks. > > > > > > > > > > > > > > > > > > > > One thing that I didn't really get to think hard about is what is the > > > > > > > effect of vmemmap manipulation wrt pfn walkers. pfn_to_page can be > > > > > > > invalid when racing with the split. How do we enforce that this won't > > > > > > > blow up? > > > > > > > > > > > > This feature depends on the CONFIG_SPARSEMEM_VMEMMAP, > > > > > > in this case, the pfn_to_page can work. The return value of the > > > > > > pfn_to_page is actually the address of it's struct page struct. > > > > > > I can not figure out where the problem is. Can you describe the > > > > > > problem in detail please? Thanks. > > > > > > > > > > struct page returned by pfn_to_page might get invalid right when it is > > > > > returned because vmemmap could get freed up and the respective memory > > > > > released to the page allocator and reused for something else. See? > > > > > > > > If the HugeTLB page is already allocated from the buddy allocator, > > > > the struct page of the HugeTLB can be freed? Does this exist? > > > > > > Nope, struct pages only ever get deallocated when the respective memory > > > (they describe) is hotremoved via hotplug. > > > > > > > If yes, how to free the HugeTLB page to the buddy allocator > > > > (cannot access the struct page)? > > > > > > But I do not follow how that relates to my concern above. > > > > Sorry. I shouldn't understand your concerns. > > > > vmemmap pages page frame > > +-----------+ mapping to +-----------+ > > | | -------------> | 0 | > > +-----------+ +-----------+ > > | | -------------> | 1 | > > +-----------+ +-----------+ > > | | -------------> | 2 | > > +-----------+ +-----------+ > > | | -------------> | 3 | > > +-----------+ +-----------+ > > | | -------------> | 4 | > > +-----------+ +-----------+ > > | | -------------> | 5 | > > +-----------+ +-----------+ > > | | -------------> | 6 | > > +-----------+ +-----------+ > > | | -------------> | 7 | > > +-----------+ +-----------+ > > > > In this patch series, we will free the page frame 2-7 to the > > buddy allocator. You mean that pfn_to_page can return invalid > > value when the pfn is the page frame 2-7? Thanks. > > No I really mean that pfn_to_page will give you a struct page pointer > from pages which you release from the vmemmap page tables. Those pages > might get reused as soon sa they are freed to the page allocator. We will remap vmemmap pages 2-7 (virtual addresses) to page frame 1. And then we free page frame 2-7 to the buddy allocator. Then accessing the struct page pointer that returned by pfn_to_page will be reflected on page frame 1. I think that here is no problem. Thanks. > -- > Michal Hocko > SUSE Labs -- Yours, Muchun