From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shaohua Li Subject: Re: [PATCH] MD: make bio mergeable Date: Thu, 28 Apr 2016 14:19:10 -0700 Message-ID: <20160428211908.GA3116523@devbig084.prn1.facebook.com> References: <384a0e0c7d6f2700aadbcbdef003cece88fa7dd7.1461626533.git.shli@fb.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Holger Kiehl Cc: linux-block@vger.kernel.org, linux-kernel , linux-raid , qkrwngud825@gmail.com, Kernel-team@fb.com, Ming Lei , Jens Axboe , Neil Brown List-Id: linux-raid.ids On Thu, Apr 28, 2016 at 08:00:22PM +0000, Holger Kiehl wrote: > Hello, > > On Mon, 25 Apr 2016, Shaohua Li wrote: > > > blk_queue_split marks bio unmergeable, which makes sense for normal bio. > > But if dispatching the bio to underlayer disk, the blk_queue_split > > checks are invalid, hence it's possible the bio becomes mergeable. > > > > In the reported bug, this bug causes trim against raid0 performance slash > > https://bugzilla.kernel.org/show_bug.cgi?id=117051 > > > This patch makes a huge difference. On a system with two Samsung 850 Pro > in a MD Raid0 setup the time for fstrim went down from ~30min to 18sec! > > However, on another system with two Intel P3700 1.6TB NVMe PCIe SSD's > also setup as one big MD Raid0, the patch does not make any difference > at all. fstrim takes more then 4 hours! Does the raid0 cross two partitions or two SSD? can you post blktrace data in the bugzilloa, I'll track the bug there. Thanks, Shaohua