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 AFF32C433F5 for ; Wed, 17 Nov 2021 06:44:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8B6BA6128B for ; Wed, 17 Nov 2021 06:44:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233822AbhKQGry (ORCPT ); Wed, 17 Nov 2021 01:47:54 -0500 Received: from mail.kernel.org ([198.145.29.99]:56412 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233802AbhKQGrx (ORCPT ); Wed, 17 Nov 2021 01:47:53 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 5D98361BD3; Wed, 17 Nov 2021 06:44:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1637131495; bh=2BahWqz3SACprKDGz/OC1O6XlOxeqnKOL020Tfr3z1M=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=A1S0fcbtI2GAWgzc+qcslMmHuvtO93bC2iQZcVO2Ln8xL/7ryWFPpIFN1K0YWZbDF nXXGA+xnz8aAqOHBhmI8tjfdC0EAuh3DFXQmB2P9VvGa01e8VLHujCTzpyRtBrYcys 7/7+IirOwjMb0Hz2CMrWazqNeAygJHp20lbHeAfw= Date: Wed, 17 Nov 2021 07:44:44 +0100 From: Greg Kroah-Hartman To: Minchan Kim Cc: Tejun Heo , LKML Subject: Re: [RFC PATCH] kernfs: release kernfs_mutex before the inode allocation Message-ID: References: <20211116194317.1430399-1-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 16, 2021 at 01:36:01PM -0800, Minchan Kim wrote: > On Tue, Nov 16, 2021 at 08:49:46PM +0100, Greg Kroah-Hartman wrote: > > On Tue, Nov 16, 2021 at 11:43:17AM -0800, Minchan Kim wrote: > > > The kernfs implementation has big lock granularity(kernfs_rwsem) so > > > every kernfs-based(e.g., sysfs, cgroup, dmabuf) fs are able to compete > > > the lock. Thus, if one of userspace goes the sleep under holding > > > the lock for a long time, rest of them should wait it. A example is > > > the holder goes direct reclaim with the lock since it needs memory > > > allocation. Let's fix it at common technique that release the lock > > > and then allocate the memory. Fortunately, kernfs looks like have > > > an refcount so I hope it's fine. > > > > > > Signed-off-by: Minchan Kim > > > --- > > > fs/kernfs/dir.c | 14 +++++++++++--- > > > fs/kernfs/inode.c | 2 +- > > > fs/kernfs/kernfs-internal.h | 1 + > > > 3 files changed, 13 insertions(+), 4 deletions(-) > > > > What workload hits this lock to cause it to be noticable? > > A app launching since it was dropping the frame since the > latency was too long. How does running a program interact with kernfs filesystems? Which one(s)? > > There was a bunch of recent work in this area to make this much more > > fine-grained, and the theoritical benchmarks that people created (adding > > 10s of thousands of scsi disks at boot time) have gotten better. > > > > But in that work, no one could find a real benchmark or use case that > > anyone could even notice this type of thing. What do you have that > > shows this? > > https://developer.android.com/studio/command-line/perfetto > https://perfetto.dev/docs/data-sources/cpu-scheduling That is links to a tool, not a test we can run ourselves. Or how about the output of that tool? > Android has perfetto tracing system and can show where processes > were stuck. This case was the lock since holder was in direct reclaim > path. Reclaim of what? What is the interaction here with kernfs? Normally this filesystem is not on any "fast paths" that I know of. More specifics would be nice :) thanks, greg k-h