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    SubjectRE: [PATCH] block: loose check on sg gap
    Date
    > From: Dexuan Cui
    > Sent: Tuesday, December 20, 2016 11:41
    > To: 'Jens Axboe' <axboe@fb.com>; Ming Lei <ming.lei@canonical.com>
    > Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>; linux-block
    > <linux-block@vger.kernel.org>; Christoph Hellwig <hch@infradead.org>;
    > Vitaly Kuznetsov <vkuznets@redhat.com>; Keith Busch
    > <keith.busch@intel.com>; Hannes Reinecke <hare@suse.de>; Mike Christie
    > <mchristi@redhat.com>; Martin K. Petersen <martin.petersen@oracle.com>;
    > Toshi Kani <toshi.kani@hpe.com>; Dan Williams <dan.j.williams@intel.com>;
    > Damien Le Moal <damien.lemoal@hgst.com>
    > Subject: RE: [PATCH] block: loose check on sg gap
    >
    > > From: Jens Axboe [mailto:axboe@fb.com]
    > > Sent: Tuesday, December 20, 2016 10:31
    > > To: Ming Lei <ming.lei@canonical.com>
    > > Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>; linux-block
    > <linux-
    > > block@vger.kernel.org>; Christoph Hellwig <hch@infradead.org>; Dexuan
    > Cui
    > > <decui@microsoft.com>; Vitaly Kuznetsov <vkuznets@redhat.com>; Keith
    > Busch
    > > <keith.busch@intel.com>; Hannes Reinecke <hare@suse.de>; Mike Christie
    > > <mchristi@redhat.com>; Martin K. Petersen
    > <martin.petersen@oracle.com>;
    > > Toshi Kani <toshi.kani@hpe.com>; Dan Williams
    > <dan.j.williams@intel.com>;
    > > Damien Le Moal <damien.lemoal@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 <axboe@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.
    >
    > -- Dexuan

    Hi Ming, Jens,
    Did you find any issue later when testing with the patch?

    May I know if it's possible to have it in 4.10 considering the above impact?

    Is it on some temporary branch of linux-block.git? Looks not.

    Thanks,
    -- Dexuan
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