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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C996DC433FE for ; Tue, 12 Oct 2021 07:50:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B6C2A60F3A for ; Tue, 12 Oct 2021 07:50:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234383AbhJLHwE (ORCPT ); Tue, 12 Oct 2021 03:52:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52076 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233988AbhJLHwC (ORCPT ); Tue, 12 Oct 2021 03:52:02 -0400 Received: from mail-ed1-x532.google.com (mail-ed1-x532.google.com [IPv6:2a00:1450:4864:20::532]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3671AC061570 for ; Tue, 12 Oct 2021 00:50:01 -0700 (PDT) Received: by mail-ed1-x532.google.com with SMTP id y12so64728742eda.4 for ; Tue, 12 Oct 2021 00:50:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=zjhSxsxPmDkUBZgqIoPJCNZSxFw5dwlvuXZheYtUcVg=; b=b2cCKTVjViEa00fDBlt1t+X+EnjEbzq3Y9qULPi0IFdRkhvDBXItqS4QyRXhWUHl3q +kO9GX5KnfKGMiHNhepZRGx4YXYfjsrj9og/StGshwDBxaxAqcRMkhMeCwuQDspinotB QmbT+wYgdIl+WdwiMXvE1b0QjUcxZRYyQR4090lYiA8cnCwIve4rYy9cKsnz7LIzpyy2 vjAUM6TOb1HYZWRY8qg/nhwuMiaXZKTEx7U25JRIkoYvqBxr33mWA+5tWlhTwqwB07eQ RMt8Ofme6aKYl3PKwDk/mrNKgVEH/XjBYTKYowXatH+16kIT3XD4gtEpCi4+pj+aqutl /CmQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=zjhSxsxPmDkUBZgqIoPJCNZSxFw5dwlvuXZheYtUcVg=; b=GRo4ON2X8A31hzMwxyg0ndqteTD4BFGIrIJlQwEBe3nmXtEA4lsgmrlqEsItS1Xrz+ Qb36UehaBhmLyCxWicJnHzkLPmKf6tnSaQRRqPe3+g+rFduADnjhKexhVi7b6vnqUgQM ilszBJQtKg+K3R/MOjKDD/xKNN8yvyrVl1JbNjxPJNQnnmoV9iyMkAIsvtG+UQN+9Q+h gPey3vFTr1KVl4+56lDkoKTopd9As5Yl7Nt7AKXDPFL6Sv6bXjj7zOOMLg/or+xZzjth v1bzwfXkXNxWinKZIYbukqWtq8ide8NRsDSx3HjZa6NLh1S30M8LjyoGsL3kFw95//a/ YLFg== X-Gm-Message-State: AOAM531wShJ8ICGEt5FnQHFqM2yASwJnjNraD2tSCYdiES9pXUPOsTez /LZnbFcDWx5Utle0qznWHwpHMw== X-Google-Smtp-Source: ABdhPJwEFW5rMXWCaGXRtspf+k4QIl8RCZntZQkLWKOktRpPjqvjyyL6uimYwSRvt4kCgM75IuJc2Q== X-Received: by 2002:a17:906:d145:: with SMTP id br5mr26348894ejb.250.1634024999730; Tue, 12 Oct 2021 00:49:59 -0700 (PDT) Received: from Iliass-MacBook-Pro.local ([62.74.11.155]) by smtp.gmail.com with ESMTPSA id m13sm5295878eda.41.2021.10.12.00.49.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 12 Oct 2021 00:49:59 -0700 (PDT) Date: Tue, 12 Oct 2021 10:49:54 +0300 From: Ilias Apalodimas To: Yunsheng Lin Cc: Jesper Dangaard Brouer , John Hubbard , davem@davemloft.net, kuba@kernel.org, brouer@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linuxarm@openeuler.org, akpm@linux-foundation.org, hawk@kernel.org, peterz@infradead.org, yuzhao@google.com, will@kernel.org, willy@infradead.org, jgg@ziepe.ca, mcroce@microsoft.com, willemb@google.com, cong.wang@bytedance.com, pabeni@redhat.com, haokexin@gmail.com, nogikh@google.com, elver@google.com, memxor@gmail.com, vvs@virtuozzo.com, linux-mm@kvack.org, edumazet@google.com, alexander.duyck@gmail.com, dsahern@gmail.com Subject: Re: [PATCH net-next -v5 3/4] mm: introduce __get_page() and __put_page() Message-ID: References: <20211009093724.10539-1-linyunsheng@huawei.com> <20211009093724.10539-4-linyunsheng@huawei.com> <62106771-7d2a-3897-c318-79578360a88a@nvidia.com> <89bcc42a-ad95-e729-0748-bf394bf770be@redhat.com> <3bba942e-eefd-7ac2-7a8c-b6c349641dd4@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3bba942e-eefd-7ac2-7a8c-b6c349641dd4@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 12, 2021 at 03:38:15PM +0800, Yunsheng Lin wrote: > On 2021/10/11 20:29, Ilias Apalodimas wrote: > > On Mon, Oct 11, 2021 at 02:25:08PM +0200, Jesper Dangaard Brouer wrote: > >> > >> > >> On 09/10/2021 21.49, John Hubbard wrote: > >>> So in case it's not clear, I'd like to request that you drop this one > >>> patch from your series. > >> > >> In my opinion as page_pool maintainer, you should also drop patch 4/4 from > >> this series. > >> > >> I like the first two patches, and they should be resend and can be applied > >> without too much further discussion. > > > > +1 > > Ok, it seems there is a lot of contention about how to avoid calling > compound_head() now. > IMHO compound head is not that heavy. So you could keep the get/put page calls as-is and worry about micro optimizations later, especially since it's intersecting with folio changes atm. > Will send out the uncontroversial one first. > Thanks! > > That's what I hinted on the previous version. The patches right now go way > > beyond the spec of page pool. We are starting to change core networking > > functions and imho we need a lot more people involved in this discussion, > > than the ones participating already. > > > > As a general note and the reason I am so hesitant, is that we are starting > > to violate layers here (at least in my opinion). When the recycling was > > added, my main concern was to keep the network stack unaware (apart from > > the skb bit). Now suddenly we need to teach frag_ref/unref internal page > > Maybe the skb recycle bit is a clever way to avoid dealing with the network > stack directly. > > But that bit might also introduce or hide some problem, like the data race > as pointed out by Alexander, and the odd using of page pool in mlx5 driver. Yea. I was always wondering if unmaping the buffers and let the network stack deal with them eventually would be a good idea (on those special cases). There's an obvious disadvantage (which imho is terrible) in this approach. Any future functions that we add in the core networking code, will need to keep that in mindxi, and unmap some random driver memory if they start playing tricks with the skb and their fragments. IOW I think this is very fragile. > > > pool counters and that doesn't feel right. We first need to prove the race > > can actually happen, before starting to change things. > > As the network stack is adding a lot of performance improvement, such as > sockmap for BPF, which may cause problem for them, will dig more to prove > that. > Ok that's something we need to look at. Are those buffers freed eventually by skb_free_head() etc? Regards /Ilias