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=-1.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 7F74FC04AB6 for ; Fri, 31 May 2019 14:48:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 44E9D26AFC for ; Fri, 31 May 2019 14:48:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20150623.gappssmtp.com header.i=@kernel-dk.20150623.gappssmtp.com header.b="dstu5uV6" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726716AbfEaOs6 (ORCPT ); Fri, 31 May 2019 10:48:58 -0400 Received: from mail-pf1-f194.google.com ([209.85.210.194]:46622 "EHLO mail-pf1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726563AbfEaOs6 (ORCPT ); Fri, 31 May 2019 10:48:58 -0400 Received: by mail-pf1-f194.google.com with SMTP id y11so6324120pfm.13 for ; Fri, 31 May 2019 07:48:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=/Z5bSUHwSp4kpRmBsObia1lPUPGkJpwlRslF3MX8yr4=; b=dstu5uV6I8AZe1524Xs0LsRfPvVcQuuv2QrR+O6sWM+CesRTgkjlrgYji8Ex3/oTlQ I5Hbtxk91nrpksAsXjsYs5ldKMmfxdd2GI3Fo7AzkVj/Z6uN+CbGN4XJxqjaciRJLfwk YQbMnw02uYLEkHOUcjgJYHojn7/LBppxV9nq10ta/kF5QQnRkdoTmngZFdeHrxDJAJJW ZzGoJD+4B8fUJ9BHDUSMskIHWlgySUg2ma5SWe9QNt+3mWfzT9rZwYPNP6Vmb4zUIlv3 GJkyqJZtS58jDZSsAsN5XjxjsldHj92SYzQKBIyLhnymsmQZrGXsXwspCkGPXVVeUB/p /7Cg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=/Z5bSUHwSp4kpRmBsObia1lPUPGkJpwlRslF3MX8yr4=; b=FOTNnrxl+UX8rsyhVMrCW4DOwDP0VfWUbbp3kWDOM8bEfqLJefVMbFH+fABRGh6mHq Opr9qqNhRFr3Ck94RBDdGitURSLr+rV0Se+cRXdVjfJDY8w3cKORk0juyN4YbIgGhuyM hc6KyekKPnBI7iDos5YUxnuZZj5qKWIrFaRgQZNipHbOIpoU55hAxRzfSJGw/LLG0ICw cee72M1kaBgJPGTBXROwecP1vre68XU68VULlVGZ0nyEpkGDg50G9o0E/nWnOFAZ7pyz 4Yz4oc8yCzcf0n3aiqEiJzFTLzHUhcPZav1hDIKRS6LIriS5w9Nm6MP/u4rQf1k8Iole fBng== X-Gm-Message-State: APjAAAWUk3LYzD/++74y/PfE8152YKe+/50XiuTn2EMZAhJLuZgBGrJR lEPw2LgxzuPzXGJ5NKX4EOvrKA== X-Google-Smtp-Source: APXvYqz43tBFILk/WNZBIPGBMolxWR2qz6wU98xoMLQPkqwbymeGztI5Belv8i1MUcfaLTEOWZdsOQ== X-Received: by 2002:a63:cc4b:: with SMTP id q11mr9747244pgi.43.1559314137820; Fri, 31 May 2019 07:48:57 -0700 (PDT) Received: from [192.168.1.158] ([65.144.74.34]) by smtp.gmail.com with ESMTPSA id k2sm5746164pjl.23.2019.05.31.07.48.55 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 31 May 2019 07:48:56 -0700 (PDT) Subject: Re: [PATCH v3 00/13] epoll: support pollable epoll from userspace To: Roman Penyaev Cc: Azat Khuzhin , Andrew Morton , Al Viro , Linus Torvalds , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org References: <20190516085810.31077-1-rpenyaev@suse.de> From: Jens Axboe Message-ID: Date: Fri, 31 May 2019 08:48:55 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190516085810.31077-1-rpenyaev@suse.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 5/16/19 2:57 AM, Roman Penyaev wrote: > Hi all, > > This is v3 which introduces pollable epoll from userspace. > > v3: > - Measurements made, represented below. > > - Fix alignment for epoll_uitem structure on all 64-bit archs except > x86-64. epoll_uitem should be always 16 bit, proper BUILD_BUG_ON > is added. (Linus) > > - Check pollflags explicitly on 0 inside work callback, and do nothing > if 0. > > v2: > - No reallocations, the max number of items (thus size of the user ring) > is specified by the caller. > > - Interface is simplified: -ENOSPC is returned on attempt to add a new > epoll item if number is reached the max, nothing more. > > - Alloced pages are accounted using user->locked_vm and limited to > RLIMIT_MEMLOCK value. > > - EPOLLONESHOT is handled. > > This series introduces pollable epoll from userspace, i.e. user creates > epfd with a new EPOLL_USERPOLL flag, mmaps epoll descriptor, gets header > and ring pointers and then consumes ready events from a ring, avoiding > epoll_wait() call. When ring is empty, user has to call epoll_wait() > in order to wait for new events. epoll_wait() returns -ESTALE if user > ring has events in the ring (kind of indication, that user has to consume > events from the user ring first, I could not invent anything better than > returning -ESTALE). > > For user header and user ring allocation I used vmalloc_user(). I found > that it is much easy to reuse remap_vmalloc_range_partial() instead of > dealing with page cache (like aio.c does). What is also nice is that > virtual address is properly aligned on SHMLBA, thus there should not be > any d-cache aliasing problems on archs with vivt or vipt caches. Why aren't we just adding support to io_uring for this instead? Then we don't need yet another entirely new ring, that's is just a little different from what we have. I haven't looked into the details of your implementation, just curious if there's anything that makes using io_uring a non-starter for this purpose? -- Jens Axboe