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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 31AE4C433F5 for ; Fri, 22 Apr 2022 17:26:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231734AbiDVR3M (ORCPT ); Fri, 22 Apr 2022 13:29:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52020 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231266AbiDVR3J (ORCPT ); Fri, 22 Apr 2022 13:29:09 -0400 Received: from mail-lj1-x236.google.com (mail-lj1-x236.google.com [IPv6:2a00:1450:4864:20::236]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7535ED5EA2 for ; Fri, 22 Apr 2022 10:26:08 -0700 (PDT) Received: by mail-lj1-x236.google.com with SMTP id h11so10477308ljb.2 for ; Fri, 22 Apr 2022 10:26:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=HJYid1oDIz8BlusNfEFWMXGaZqmdNR6muh9voapRylw=; b=AtB9Znor7qBu+dy6JyI664aV539rkJ0X3gjGNPpVOeHFyCEP/I/Hsv4NfoT9i7Hzxn Nl6P6cq/S2hxwrDu/aRQUrnmu+cNn5TBofpy24Mmqb+Z2ByL1r6A/ZSvapmDfqQRkP1L ANb2GP8Mu3sRwgI8T4O7seKqxD0Du4+OIqpag= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=HJYid1oDIz8BlusNfEFWMXGaZqmdNR6muh9voapRylw=; b=OmVIzJapFzMd+0o5gKZgtqEOAJEQoK3Gh8ioR/pn9Ic+BeU2qZFDqPTmOZxePenqkH XR97UcT0QjFIJnYnLWwcl3NuskG09aO4iPnyzCSJSSHwNcRvkqb+8RsT8IS0vpz2FmBu pMp7RNu42neNgPoCZ+SqkLH4C3t+TAXfY2CpPRkDS7Z61O8ePmxMP4CisD8hf3NJ/xM6 k8maR+U/YDYY5hhtysryr9n97erw0pz/ZKBReVh8huV8tvQBU0p1/F35WaCWcEqT7UXf FP/C+YbHJ5jIDuUpGDaq8vDMoL2aXVGgjK7DikCQOJhoL6MBp998YU+443BeGZDPvrtw kwFA== X-Gm-Message-State: AOAM533w8oEsDtZCuDLz5JK9BVlYbK+0TcqnVlwz5rMG3ycUuapKBiGv ldDqDjunqfXcDZyYuc57ivUDDXLXilujp+spkl4= X-Google-Smtp-Source: ABdhPJxiW1DbSEQmnUPWKQTa8bR1T5IkOcmxe/nUv99KWYYFEqEED1sm0zC3eEvOBA739uTinAfCMg== X-Received: by 2002:a2e:bd13:0:b0:244:da2f:ff4d with SMTP id n19-20020a2ebd13000000b00244da2fff4dmr3563694ljq.213.1650648235626; Fri, 22 Apr 2022 10:23:55 -0700 (PDT) Received: from mail-lj1-f174.google.com (mail-lj1-f174.google.com. [209.85.208.174]) by smtp.gmail.com with ESMTPSA id bj37-20020a2eaaa5000000b0024dd3537e93sm283376ljb.114.2022.04.22.10.23.53 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 22 Apr 2022 10:23:53 -0700 (PDT) Received: by mail-lj1-f174.google.com with SMTP id bn33so10449978ljb.6 for ; Fri, 22 Apr 2022 10:23:53 -0700 (PDT) X-Received: by 2002:a2e:8245:0:b0:24b:48b1:a1ab with SMTP id j5-20020a2e8245000000b0024b48b1a1abmr3347370ljh.152.1650648232816; Fri, 22 Apr 2022 10:23:52 -0700 (PDT) MIME-Version: 1.0 References: <20220420073717.GD16310@xsang-OptiPlex-9020> In-Reply-To: From: Linus Torvalds Date: Fri, 22 Apr 2022 10:23:36 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [fs/pipe] 5a519c8fe4: WARNING:at_mm/page_alloc.c:#__alloc_pages To: Andrei Vagin Cc: kernel test robot , Dmitry Safonov <0x7f454c46@gmail.com>, Alexander Viro , Andrew Morton , LKML , lkp@lists.01.org, kernel test robot , Mike Rapoport , Pavel Emelyanov Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 21, 2022 at 10:23 PM Andrei Vagin wrote: > > The big advantage of vmsplice is that it can attach real user pages into > a pipe and then any following changes of these pages by the process > don't trigger any allocations and extra copies of data. vmsplice in this > case is fast. After splicing pages to pipes, we resume a process and > splice pages from pipes to a socket or a file. The whole process of > dumping process pages is zero-copy. Hmm. What happens if you just use /proc//mem? That just takes a reference to the tsk->mm. No page copies at all. After that you can do anything you want to that mm. Well, anything a /proc//mm fd allows, which is mainly read and write. But it stays around for as long as you keep it open, and fundamentally stays coherent with that mm, because it *is* that mm. And it doesn't affect anything else, because all it literally has is that mm_struct pointer. Linus