From mboxrd@z Thu Jan 1 00:00:00 1970 From: Linus Torvalds Subject: Re: [PATCH] fs-writeback: drop wb->list_lock during blk_finish_plug() Date: Fri, 11 Sep 2015 14:04:13 -0700 Message-ID: References: <20150911193747.GA4150@ret.masoncoding.com> <55F33C2B.1010508@fb.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: Chris Mason , LKML , linux-fsdevel , Dave Chinner , Neil Brown , Jan Kara , Christoph Hellwig To: Josef Bacik Return-path: In-Reply-To: <55F33C2B.1010508@fb.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Fri, Sep 11, 2015 at 1:40 PM, Josef Bacik wrote: > > So we talked about this when we were trying to figure out a solution. The > problem with this approach is now we have a plug that covers multiple super > blocks (__writeback_inodes_wb loops through the sb's starts writeback), > which is likely to give us crappier performance than no plug at all. Why would that be? Either they are on separate disks, and the IO is all independent anyway, and at most it got started by some (small) CPU-amount later. Actual throughput should be the same. No? Or the filesystems are on the same disk, in which case it should presumably be a win to submit the IO together. Of course, actual numbers would be the deciding factor if this really is noticeable. But "cleaner code and saner locking" is definitely an issue at least for me. Linus