> From: Jens Axboe [mailto:ax...@fb.com] > Sent: Tuesday, December 20, 2016 10:31 > To: Ming Lei <ming....@canonical.com> > Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>; linux-block > <linux- > bl...@vger.kernel.org>; Christoph Hellwig <h...@infradead.org>; Dexuan Cui > <de...@microsoft.com>; Vitaly Kuznetsov <vkuzn...@redhat.com>; Keith Busch > <keith.bu...@intel.com>; Hannes Reinecke <h...@suse.de>; Mike Christie > <mchri...@redhat.com>; Martin K. Petersen <martin.peter...@oracle.com>; > Toshi Kani <toshi.k...@hpe.com>; Dan Williams <dan.j.willi...@intel.com>; > Damien Le Moal <damien.lem...@hgst.com> > Subject: Re: [PATCH] block: loose check on sg gap > > On 12/19/2016 07:07 PM, Ming Lei wrote: > > On Sun, Dec 18, 2016 at 12:49 AM, Jens Axboe <ax...@fb.com> wrote: > >> On 12/17/2016 03:49 AM, Ming Lei wrote: > >>> If the last bvec of the 1st bio and the 1st bvec of the next > >>> bio are contineous physically, and the latter can be merged > >>> to last segment of the 1st bio, we should think they don't > >>> violate sg gap(or virt boundary) limit. > >>> > >>> Both Vitaly and Dexuan reported lots of unmergeable small bios > >>> are observed when running mkfs on Hyper-V virtual storage, and > >>> performance becomes quite low, so this patch is figured out for > >>> fixing the performance issue. > >>> > >>> The same issue should exist on NVMe too sine it sets virt boundary too. > >> > >> It looks pretty reasonable to me. I'll queue it up for some testing, > >> changes like this always make me a little nervous. > > > > Understood. > > > > But given it is still in early stage of 4.10 cycle, seems fine to expose > > it now, and we should have enough time to fix it if there might be > > regressions. > > > > BTW, it passes my xfstest(ext4) over sata/NVMe. > > It's been fine here in testing, too. I'm not worried about performance > regressions, those we can always fix. Merging makes me worried about > corruption, and those regressions are much worse. > > Any reason we need to rush this? I'd be more comfortable pushing this to > 4.11, unless there are strong reasons this should make 4.10. > > -- > Jens Axboe
Hi Jens, As far as I know, the patch is important to popular Linux distros, e.g. at least Ubuntu 14.04.5, 16.x and RHEL 7.3, when they run on Hyper-V/Azure, because they can suffer from a pretty bad throughput/latency in some cases, e.g. mkfs.ext4 for a 100GB partition can take 8 minutes, but with the patch, it only takes 1 second. Thanks, -- Dexuan
