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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 3E1F9C433FF for ; Tue, 13 Aug 2019 11:57:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0894720679 for ; Tue, 13 Aug 2019 11:57:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ziepe.ca header.i=@ziepe.ca header.b="ap0SmPcZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727692AbfHML5K (ORCPT ); Tue, 13 Aug 2019 07:57:10 -0400 Received: from mail-qt1-f194.google.com ([209.85.160.194]:33423 "EHLO mail-qt1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727342AbfHML5J (ORCPT ); Tue, 13 Aug 2019 07:57:09 -0400 Received: by mail-qt1-f194.google.com with SMTP id v38so13616076qtb.0 for ; Tue, 13 Aug 2019 04:57:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ziepe.ca; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=RPb0NU5H2rzwjdvr45r58ZWni2Zoy4JljRGSpgnMMr4=; b=ap0SmPcZPZ6NNFvNyFkpypRbg36yi8bdsTd4/F6gQQqPPgiM5IjDvTKZEGGxca8l8F u5EQEn7sEyhGruMuB7cjg3kUgzh9Cv/quO6ECF3rbawY4hb6Yw2dyN9iU6PgCvTDOCh0 xsYZVNW0ajla3uTLaTh6ZCITFtrsONP4+81D6sumJLjqzxf2snBDmJYrwx6qXccYld+H swJwSMjlc5QmHizDCiZoTu8O5ptOxdiKgiKAZ9i3JGi/jhbj1siIrzDAKpRTStg72MQw /hWyMVuaK40viEpVJr1GXiLhMU2L4bLITv7lm7rfgwRXFHTHOxuSU5tATEjLqz3Rmkx9 LONQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=RPb0NU5H2rzwjdvr45r58ZWni2Zoy4JljRGSpgnMMr4=; b=bWDGpD87Thgsg+ZhLIKJ1yDpDw19OcU7czF/mfNriaErTdqWhKS8LNywd1QANUW+Wv j2Z9gtO5jXmaXM5yutjxjvH3ixfDDQAzRlCfwTmmjbFMeF81lxOJ6vR35NITwBsPzk92 H5LpA/z1BhGiwrnspzDA533WfpinOLerCAjF06gozZHNkI5Al4/nUdVnEbfqBOAzGmt7 7TIXmSzMyqO1BdNbiPMiSuzAMk98nn/rl5/v0r7PMqxMDJd1hOBMZ95zkImAP4mMkoKD WKs26mhZmWY5chAh/VCTiBwLOBl9aASt1d1WEefG/vyPtRCFHV/eAMs2zyxzqO1Iycka Ic/w== X-Gm-Message-State: APjAAAXzYCHUG5zEYDCMNeoF3qS+5gLs681+eak4MFpJvxINmGM1AY0U bpisqISZ9ZwkJ2fN/gHD+q+2Zg== X-Google-Smtp-Source: APXvYqyQLbr3IuoVdbXppS/ZGOesGhtgbHcYTwB9ezrUQfPYFcx2A9k+2h1mf3jK0ev1zMtBSQ9gpg== X-Received: by 2002:a0c:f193:: with SMTP id m19mr33863324qvl.20.1565697428498; Tue, 13 Aug 2019 04:57:08 -0700 (PDT) Received: from ziepe.ca (hlfxns017vw-156-34-55-100.dhcp-dynamic.fibreop.ns.bellaliant.net. [156.34.55.100]) by smtp.gmail.com with ESMTPSA id r4sm69930362qta.93.2019.08.13.04.57.07 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 13 Aug 2019 04:57:07 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1hxVQJ-0007sn-HH; Tue, 13 Aug 2019 08:57:07 -0300 Date: Tue, 13 Aug 2019 08:57:07 -0300 From: Jason Gunthorpe To: Jason Wang Cc: "Michael S. Tsirkin" , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH V5 0/9] Fixes for vhost metadata acceleration Message-ID: <20190813115707.GC29508@ziepe.ca> References: <20190809054851.20118-1-jasowang@redhat.com> <20190810134948-mutt-send-email-mst@kernel.org> <360a3b91-1ac5-84c0-d34b-a4243fa748c4@redhat.com> <20190812054429-mutt-send-email-mst@kernel.org> <20190812130252.GE24457@ziepe.ca> <9a9641fe-b48f-f32a-eecc-af9c2f4fbe0e@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9a9641fe-b48f-f32a-eecc-af9c2f4fbe0e@redhat.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 13, 2019 at 04:31:07PM +0800, Jason Wang wrote: > What kind of issues do you see? Spinlock is to synchronize GUP with MMU > notifier in this series. A GUP that can't sleep can't pagefault which makes it a really weird pattern > Btw, back to the original question. May I know why synchronize_rcu() is not > suitable? Consider: We already went over this. You'd need to determine it doesn't somehow deadlock the mm on reclaim paths. Maybe it is OK, the rcq_gq_wq is marked WQ_MEM_RECLAIM at least.. I also think Michael was concerned about the latency spikes a long RCU delay would cause. Jason