From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933239AbaFILLL (ORCPT ); Mon, 9 Jun 2014 07:11:11 -0400 Received: from mail-wg0-f46.google.com ([74.125.82.46]:48084 "EHLO mail-wg0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932067AbaFILLJ convert rfc822-to-8bit (ORCPT ); Mon, 9 Jun 2014 07:11:09 -0400 Content-Type: text/plain; charset=US-ASCII Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.2\)) Subject: Re: [fuse-devel] [PATCH 0/5] fuse: close file synchronously (v2) From: John Muir In-Reply-To: <5395906F.3070903@parallels.com> Date: Mon, 9 Jun 2014 13:11:06 +0200 Cc: Miklos Szeredi , fuse-devel , Linux List Content-Transfer-Encoding: 7BIT Message-Id: <1AC1913F-47DF-4707-8E27-F2E7334CE2D6@jmuir.com> References: <20140606132541.30321.68679.stgit@localhost.localdomain> <53956730.1070302@parallels.com> <5395906F.3070903@parallels.com> To: Maxim Patlasov X-Mailer: Apple Mail (2.1878.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2014.06.09, at 12:46 , Maxim Patlasov wrote: > On 06/09/2014 01:26 PM, John Muir wrote: >> On 2014.06.09, at 9:50 , Maxim Patlasov wrote: >> >>> On 06/06/2014 05:51 PM, John Muir wrote: >>>> On 2014.06.06, at 15:27 , Maxim Patlasov wrote: >>>> >>>>> The patch-set resolves the problem by making fuse_release synchronous: >>>>> wait for ACK from userspace for FUSE_RELEASE if the feature is ON. >>>> Why not make this feature per-file with a new flag bit in struct fuse_file_info rather than as a file-system global? >>> I don't expect a great demand for such a granularity. File-system global "close_wait" conveys a general user expectation about filesystem behaviour in distributed environment: if you stopped using a file on given node, whether it means that the file is immediately accessible from another node. >>> >> By user do you mean the end-user, or the implementor of the file-system? It seems to me that the end-user doesn't care, and just wants the file-system to work as expected. I don't think we're really talking about the end-user. > > No, this is exactly about end-user expectations. Imagine a complicated heavy-loaded shared storage where handling FUSE_RELEASE in userspace may take a few minutes. In close_wait=0 case, an end-user who has just called close(2) has no idea when it's safe to access the file from another node or even when it's OK to umount filesystem. I think we're saying the same thing here from different perspectives. The end-user wants the file-system to operate with the semantics you describe, but I don't think it makes sense to give the end-user control over those semantics. The file-system itself should be implemented that way, or not, or per-file If it's a read-only file, then does this not add the overhead of having the kernel wait for the user-space file-system process to respond before closing it. In my experience, there is actually significant cost to the kernel to user-space messaging in FUSE when manipulating thousands of files. > >> >> The implementor of a file-system, on the other hand, might want the semantics for close_wait on some files, but not on others. Won't there be a performance impact? Some distributed file-systems might want this on specific files only. Implementing it as a flag on the struct fuse_file_info gives the flexibility to the file-system implementor. > > fuse_file_info is an userspace structure, in-kernel fuse knows nothing about it. In close_wait=1 case, nothing prevents a file-system implementation from ACK-ing FUSE_RELEASE request immediately (for specific files) and schedule actual handling for future processing. Of course you know I meant that you'd add another flag to both fuse_file_info, and in the kernel equivalent for those flags which is struct fuse_open_out -> open_flags. This is where other such per file options are specified such as whether or not to keep the in-kernal cache for a file, whether or not to allow direct-io, and whether or not to allow seek. Anyway, I guess you're the one doing all the work on this and if you have a particular implementation that doesn't require such fine-grained control, and no one else does then it's up to you. I'm just trying to show an alternative implementation that gives the file-system implementor more control while keeping the ability to meet user expectations. Regards, John. -- John Muir - john@jmuir.com +32 491 64 22 76