From: Jan Kara Subject: Re: [PATCH 2/3] vfs, writeback: replace FS_CGROUP_WRITEBACK with MS_CGROUPWB Date: Mon, 15 Jun 2015 13:39:49 +0200 Message-ID: <20150615113949.GC4368@quack.suse.cz> References: <1434146254-26220-1-git-send-email-tj@kernel.org> <1434146254-26220-3-git-send-email-tj@kernel.org> <20150613161608.GA29414@infradead.org> <20150614054236.GA9662@mtj.duckdns.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Christoph Hellwig , axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Alexander Viro , Jan Kara , linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Tejun Heo Return-path: Content-Disposition: inline In-Reply-To: <20150614054236.GA9662-qYNAdHglDFBN0TnZuCh8vA@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-ext4.vger.kernel.org On Sun 14-06-15 00:42:36, Tejun Heo wrote: > Hello, Christoph. > > On Sat, Jun 13, 2015 at 09:16:08AM -0700, Christoph Hellwig wrote: > > On Fri, Jun 12, 2015 at 04:57:33PM -0500, Tejun Heo wrote: > > > FS_CGROUP_WRITEBACK indicates whether a file_system_type supports > > > cgroup writeback; however, different super_blocks of the same > > > file_system_type may or may not support cgroup writeback depending on > > > filesystem options. This patch replaces FS_CGROUP_WRITEBACK with a > > > kernel-internal super_block->s_flags MS_CGROUPWB. The concatenated > > > and abbreviated name is for consistency with other MS_* flags. > > > > Nak. As the uapi part makes it obvious the MS_ namespace is part > > of the userspace ABI. Please add a new in-kernel flags field instead. > > Are MS_ACTIVE and MS_BORN part of userpace ABI? They seem pretty > internal. I don't mind introducing a new internal flag field but it's > weird to put this single flag there with other internal flags in > ->s_flags. So you are right that there are other internal flags allocated from the top of the i_flags field, however we are pretty much running out of the flags available for the ABI so it's better to move internal flags elsewhere as that's simpler than creating a new ABI for mount... > Assuming we add a new field, how do sb->s_iflags and SB_I_XXX sound? > Any better suggestions? Looks good to me. Honza -- Jan Kara SUSE Labs, CR