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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 0CC7BC433DF for ; Wed, 12 Aug 2020 08:37:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D598A20781 for ; Wed, 12 Aug 2020 08:37:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="key not found in DNS" (0-bit key) header.d=szeredi.hu header.i=@szeredi.hu header.b="AcC/qQQC" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727024AbgHLIhW (ORCPT ); Wed, 12 Aug 2020 04:37:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48810 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726976AbgHLIhV (ORCPT ); Wed, 12 Aug 2020 04:37:21 -0400 Received: from mail-ej1-x644.google.com (mail-ej1-x644.google.com [IPv6:2a00:1450:4864:20::644]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 844B0C061787 for ; Wed, 12 Aug 2020 01:37:20 -0700 (PDT) Received: by mail-ej1-x644.google.com with SMTP id t10so1329285ejs.8 for ; Wed, 12 Aug 2020 01:37:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=szeredi.hu; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=e5lKpdbRMPYHAYu1ae51I164qapzjNwIVzhn7ZJhmbg=; b=AcC/qQQCnxrUQDrRulzph4bIrPpKQ4hbVAqb0dQpE0YjsJg0S4AcKPqmLXQnYuZ8gQ 9rMS2fX/xoMespxJ1EdabWK4zL1o2n2eaJ+IDZKcNAadf3DO9VvJI4IyDPUvT+oct/lD KK1tAvYAp2gilfvh3FiKoGKiqOV2rTwVpP3Es= 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=e5lKpdbRMPYHAYu1ae51I164qapzjNwIVzhn7ZJhmbg=; b=UJYI1tQ6+KyS2LRhF7sxySAaVmz8mBEhp3eGqBL9ipINz5jk9hwmarVFAyvlwjprV7 RTNdZNn1MfrhsEuH+UhOdPZx/5xUA8ZYBUqwfCMnvS2QkmrrMUwmC0RvH8twJ4i4bVsx m9FaTGFUSw4DDRlglbpyK+M/quRUWJfW0xWNKztB9oDtyVZK1cOejJIHM1tIj6x0b40j bEk5TJPy6qE2RiEE2Zde6Yb9kQ4KULeJ364BPswfdHSUS5TdNDFQs1UZp9jFXVDjbwLl KbCsr43XMA9t6x9AXNF0hS+hVDHE/W+Zs/2SBj7JGUT7v8i+vMgDfA5xiftV+lJqegiv +cIw== X-Gm-Message-State: AOAM532N8NSDOHyK56uJYuny6Bv8som2mjVeFTou4xND/gj/4GP8BbgA kYkQEoo4VIcg5qrNbMWI0utRGp93xURTXNE+Qc9Je+HFOgo= X-Google-Smtp-Source: ABdhPJzWseLvjIX9yMZK1gWPtlrnfWCFKz8bLBOi+m92pGbohAATJNi/NlUhIAcvWT8riat4xaFeXZBq0E4EMOYrDOI= X-Received: by 2002:a17:906:b2d7:: with SMTP id cf23mr29546689ejb.113.1597221439198; Wed, 12 Aug 2020 01:37:19 -0700 (PDT) MIME-Version: 1.0 References: <1842689.1596468469@warthog.procyon.org.uk> <1845353.1596469795@warthog.procyon.org.uk> <20200811135419.GA1263716@miu.piliscsaba.redhat.com> <52483.1597190733@warthog.procyon.org.uk> <98802.1597220949@warthog.procyon.org.uk> In-Reply-To: <98802.1597220949@warthog.procyon.org.uk> From: Miklos Szeredi Date: Wed, 12 Aug 2020 10:37:08 +0200 Message-ID: Subject: Re: file metadata via fs API (was: [GIT PULL] Filesystem Information) To: David Howells Cc: Linus Torvalds , linux-fsdevel , Al Viro , Karel Zak , Jeff Layton , Miklos Szeredi , Nicolas Dichtel , Christian Brauner , Lennart Poettering , Linux API , Ian Kent , LSM , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 12, 2020 at 10:29 AM David Howells wrote: > > Miklos Szeredi wrote: > > > Worried about performance? Io-uring will allow you to do all those > > five syscalls (or many more) with just one I/O submission. > > io_uring isn't going to help here. We're talking about synchronous reads. > AIUI, you're adding a couple more syscalls to the list and running stuff in a > side thread to save the effort of going in and out of the kernel five times. > But you still have to pay the set up/tear down costs on the fds and do the > pathwalks. io_uring doesn't magically make that cost disappear. > > io_uring also requires resources such as a kernel accessible ring buffer to > make it work. > > You're proposing making everything else more messy just to avoid a dedicated > syscall. Could you please set out your reasoning for that? a) A dedicated syscall with a complex binary API is a non-trivial maintenance burden. b) The awarded performance boost is not warranted for the use cases it is designed for. Thanks, Miklos