From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Piggin Subject: Re: [PATCH 13/18] fs: split locking of inode writeback and LRU lists Date: Sat, 16 Oct 2010 18:57:13 +1100 Message-ID: <20101016075713.GQ19147@amd> References: <1286515292-15882-1-git-send-email-david@fromorbit.com> <1286515292-15882-14-git-send-email-david@fromorbit.com> <20101008074243.GB24089@infradead.org> <20101008080018.GV4681@dastard> <20101008081816.GA17577@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Dave Chinner , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: Christoph Hellwig Return-path: Content-Disposition: inline In-Reply-To: <20101008081816.GA17577@infradead.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Fri, Oct 08, 2010 at 04:18:16AM -0400, Christoph Hellwig wrote: > On Fri, Oct 08, 2010 at 07:00:18PM +1100, Dave Chinner wrote: > > > > > > > > - if (inode->i_state & (I_NEW | I_WILL_FREE)) { > > > > + if (inode->i_state & (I_NEW | I_WILL_FREE | I_FREEING)) { > > > > requeue_io(inode); > > > > continue; > > > > } > > > > > > What does this have to do with the rest of the patch? > > > > That's because there's now a window between setting I_FREEING and taking > > the inode off the writeback list which means that we can see inodes > > in that state here. Generally it means that the code setting > > I_FREEING is spinning waiting for the wb->b_lock that this thread > > currently holds so it can be removed from the list.. Hence the requeue > > to move the inode out of the way and keep processing inodes for > > writeback. > > That needs some documentation both in the changelog and in the code > I think. This is another instance where the irregular i_lock locking is making these little subtleties to the locking. I think that is actually much worse for maintainence/complexity than a few trylocks which can be mostly removed with rcu anyway (which are obvious because of the well documented lock order).