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Date:   Wed, 26 Sep 2018 20:00:12 +0300
From:   Leon Romanovsky <leon@kernel.org>
To:     Jan Dakinevich <jan.dakinevich@virtuozzo.com>
Cc:     Jason Gunthorpe <jgg@ziepe.ca>, Doug Ledford <dledford@redhat.com>,
        Yishai Hadas <yishaih@mellanox.com>,
        Parav Pandit <parav@mellanox.com>,
        Mark Bloch <markb@mellanox.com>,
        Daniel Jurgens <danielj@mellanox.com>,
        Kees Cook <keescook@chromium.org>,
        Kamal Heib <kamalheib1@gmail.com>,
        Bart Van Assche <bvanassche@acm.org>,
        linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org,
        Denis Lunev <den@virtuozzo.com>,
        Konstantin Khorenko <khorenko@virtuozzo.com>
Subject: Re: [PATCH 0/4] IB: decrease large contigous allocation
Message-ID: <20180926170012.GA1689@mtr-leonro.mtl.com>
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On Wed, Sep 26, 2018 at 06:43:42PM +0300, Jan Dakinevich wrote:
> On Wed, 19 Sep 2018 00:23:51 +0300
> Leon Romanovsky <leon@kernel.org> wrote:
>
> > On Tue, Sep 18, 2018 at 08:46:23AM -0600, Jason Gunthorpe wrote:
> > > On Tue, Sep 18, 2018 at 04:03:42PM +0300, Jan Dakinevich wrote:
> > > > The size of mlx4_ib_device became too large to be allocated as
> > > > whole contigous block of memory. Currently it takes about 55K. On
> > > > architecture with 4K page it means 3rd order.
> > > >
> > > > This patch series makes an attempt to split mlx4_ib_device into
> > > > several parts and allocate them with less expensive kvzalloc
> > >
> > > Why split it up? Any reason not to just allocate the whole thing
> > > with kvzalloc?
> >
>
> This allocation could be triggered by userspace. It means that at
> _arbitrary_ time kernel could be asked for high order allocation.
>
> This case is considered unacceptable for system under significant load,
> since kernel would try to satisfy this memory request wasting the
> overall performance.

In such case, you won't do very much with mlx4_ib device. It will be
unusable.

>
> > And before we are rushing to dissect mlx4_ib driver, can you
> > explain the rationale behind this change? The mlx4_ib driver
> > represents high-performance device which needs enough memory
> > resources to operate. Those devices are limited by number
> > of PCIs and SRIOV VFs (upto 126) and very rare allocated/deallocated.
> >
> > I would like to see real rationale behind such change.
> >
> > Thanks
> >
> > >
> > > Jason
>
>
>
> --
> Best regards
> Jan Dakinevich

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