linux-kernel - Re: [PATCH 0/4] IB: decrease large contigous allocation

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Message-ID: <20180918212351.GB3661@mtr-leonro.mtl.com>
Date:   Wed, 19 Sep 2018 00:23:51 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Jan Dakinevich <jan.dakinevich@...tuozzo.com>,
        Doug Ledford <dledford@...hat.com>,
        Yishai Hadas <yishaih@...lanox.com>,
        Parav Pandit <parav@...lanox.com>,
        Mark Bloch <markb@...lanox.com>,
        Daniel Jurgens <danielj@...lanox.com>,
        Kees Cook <keescook@...omium.org>,
        Kamal Heib <kamalheib1@...il.com>,
        Bart Van Assche <bvanassche@....org>,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        Denis Lunev <den@...tuozzo.com>,
        Konstantin Khorenko <khorenko@...tuozzo.com>
Subject: Re: [PATCH 0/4] IB: decrease large contigous allocation

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?

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

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