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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL 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 37B0FC433DB for ; Tue, 23 Mar 2021 18:48:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F1601619C1 for ; Tue, 23 Mar 2021 18:48:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231553AbhCWSsZ (ORCPT ); Tue, 23 Mar 2021 14:48:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48888 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231834AbhCWSsH (ORCPT ); Tue, 23 Mar 2021 14:48:07 -0400 Received: from mail-pj1-x1033.google.com (mail-pj1-x1033.google.com [IPv6:2607:f8b0:4864:20::1033]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CA1A1C061763 for ; Tue, 23 Mar 2021 11:48:06 -0700 (PDT) Received: by mail-pj1-x1033.google.com with SMTP id kk2-20020a17090b4a02b02900c777aa746fso10510240pjb.3 for ; Tue, 23 Mar 2021 11:48:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=W0hZGL9ovQy+jWSfLjuO4yiUfJKwclwtM7TKVF346ck=; b=ZV0TRepGN/bTRrghylVvoSE2ass/5JiPwc7sWV/wAQVPb1uoehbKFxYd4S32T2g/0y bi8QRSGC4kiddQG52GuTZgZjLEO4L9GEbm0s0/mkY8Zy6+prXQuZMGBVscsMwTRldNqu lyWIYuzOG0oWrteGqrjaL6MJtGAJiNp/0XVN+6Of7kEDrx+5blNdgrFJEx40IIDQ0W+z cmAArxmrCm2xFu8htn/jaTt9xHXJKScLEwYLKM9GS7/7wd/U7vR/RgVPpaGOSmapqvr1 +6LH315iekrNT5vGiRN5yU6KXXK5v2ezMT+076k3qWVhPbW0Geaur0UYFWCw4Pb+1DX3 6Vtg== 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=W0hZGL9ovQy+jWSfLjuO4yiUfJKwclwtM7TKVF346ck=; b=CQnUuw/M4Y1eAw1dTLoZz17RXaXDHVVXw1/gKXE481xzd8vJsvzT+7n6W6foo1E+Nc v69dFOrXs84XOiO/+cOVY30n7a6zw7Vt3kcz5SXDS0bx8wtvnSiP234mO6IlAXrhbAPT uZo/B//JIgOJ6dqx8sQvI9BuOazdckYIGIG/1nX/fNp8ejBsFcMR6TfGwNv4/IWGo9nY XQzmLcmVa/BWD9a8jhOGEy8E2vMxxIYdapRk2MJj/BNUUUpL65TIttRHYxM2RoZ3jxP9 QVGGZaeDV48wv5lpacrgt3mx7bUQnWHo0koRSCZNDV72zU/m/RHTsSySfuoLb3bZ24Gr R8cg== X-Gm-Message-State: AOAM532iJ+AVyyv514I8q2RXPLsbZkX1L7H/We3WPnXlDif6EU8yqDeS ShYTCmu2WqfE85Cx+g2FCytiQj0XQwBgpQKP13PA+w== X-Google-Smtp-Source: ABdhPJy58JffI7SATii7n67BekyxmpIkXD68FhgTDdhjmi8lNU5f3dTxTfW+xxhQJKHw4a/ukBsfSA8VFunC//JWCLg= X-Received: by 2002:a17:90b:947:: with SMTP id dw7mr5892929pjb.178.1616525286054; Tue, 23 Mar 2021 11:48:06 -0700 (PDT) MIME-Version: 1.0 References: <20210316041645.144249-1-arjunroy.kdev@gmail.com> In-Reply-To: From: Arjun Roy Date: Tue, 23 Mar 2021 11:47:54 -0700 Message-ID: Subject: Re: [mm, net-next v2] mm: net: memcg accounting for TCP rx zerocopy To: Michal Hocko Cc: Johannes Weiner , Arjun Roy , Andrew Morton , David Miller , netdev , Linux Kernel Mailing List , Cgroups , Linux MM , Shakeel Butt , Eric Dumazet , Soheil Hassas Yeganeh , Jakub Kicinski , Yang Shi , Roman Gushchin Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 23, 2021 at 7:34 AM Michal Hocko wrote: > > On Wed 17-03-21 18:12:55, Johannes Weiner wrote: > [...] > > Here is an idea of how it could work: > > > > struct page already has > > > > struct { /* page_pool used by netstack */ > > /** > > * @dma_addr: might require a 64-bit value even on > > * 32-bit architectures. > > */ > > dma_addr_t dma_addr; > > }; > > > > and as you can see from its union neighbors, there is quite a bit more > > room to store private data necessary for the page pool. > > > > When a page's refcount hits zero and it's a networking page, we can > > feed it back to the page pool instead of the page allocator. > > > > From a first look, we should be able to use the PG_owner_priv_1 page > > flag for network pages (see how this flag is overloaded, we can add a > > PG_network alias). With this, we can identify the page in __put_page() > > and __release_page(). These functions are already aware of different > > types of pages and do their respective cleanup handling. We can > > similarly make network a first-class citizen and hand pages back to > > the network allocator from in there. > > For compound pages we have a concept of destructors. Maybe we can extend > that for order-0 pages as well. The struct page is heavily packed and > compound_dtor shares the storage without other metadata > int pages; /* 16 4 */ > unsigned char compound_dtor; /* 16 1 */ > atomic_t hpage_pinned_refcount; /* 16 4 */ > pgtable_t pmd_huge_pte; /* 16 8 */ > void * zone_device_data; /* 16 8 */ > > But none of those should really require to be valid when a page is freed > unless I am missing something. It would really require to check their > users whether they can leave the state behind. But if we can establish a > contract that compound_dtor can be always valid when a page is freed > this would be really a nice and useful abstraction because you wouldn't > have to care about the specific type of page. > > But maybe I am just overlooking the real complexity there. > -- For now probably the easiest way is to have network pages be first class with a specific flag as previously discussed and have concrete handling for it, rather than trying to establish the contract across page types. Thanks, -Arjun > Michal Hocko > SUSE Labs