From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754933AbaFIMAR (ORCPT ); Mon, 9 Jun 2014 08:00:17 -0400 Received: from relay.parallels.com ([195.214.232.42]:58045 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752662AbaFIMAO (ORCPT ); Mon, 9 Jun 2014 08:00:14 -0400 Message-ID: <5395A1CB.3070504@parallels.com> Date: Mon, 9 Jun 2014 16:00:11 +0400 From: Maxim Patlasov User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: John Muir CC: Miklos Szeredi , fuse-devel , Linux List Subject: Re: [fuse-devel] [PATCH 0/5] fuse: close file synchronously (v2) References: <20140606132541.30321.68679.stgit@localhost.localdomain> <53956730.1070302@parallels.com> <5395906F.3070903@parallels.com> <1AC1913F-47DF-4707-8E27-F2E7334CE2D6@jmuir.com> In-Reply-To: <1AC1913F-47DF-4707-8E27-F2E7334CE2D6@jmuir.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.30.24.252] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/09/2014 03:11 PM, John Muir wrote: > 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. Thank you, John. That's really depends on whether someone else wants fine-grained control or not. I'm generally OK to re-work the patch-set if more requesters emerge. Thanks, Maxim