linux-kernel - Re: [PATCH v2 2/3] spi: allocate spi_board

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Message-ID: <20170228221245.GL20776@dtor-ws>
Date:   Tue, 28 Feb 2017 14:12:45 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Mark Brown <broonie@...nel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] spi: allocate spi_board_info entries one by one

On Tue, Feb 28, 2017 at 09:15:12PM +0100, Geert Uytterhoeven wrote:
> On Tue, Feb 28, 2017 at 7:54 PM, Mark Brown <broonie@...nel.org> wrote:
> > On Tue, Feb 28, 2017 at 10:24:17AM -0800, Dmitry Torokhov wrote:
> >> On Tue, Feb 28, 2017 at 09:16:50AM +0000, Mark Brown wrote:
> >> > On Mon, Feb 27, 2017 at 08:18:56PM -0800, Dmitry Torokhov wrote:
> >> > > Lists of spi_board_info entries registered with spi_register_board_info()
> >> > > can be quite long; instead of forcing memory allocator find contagious
> >
> >> > Do you have numbers on that?
> >
> >> Hm, so the largest array seems to be in
> >> arch/blackfin/mach-bf537/boards/stamp.c at max of 43 entries. The new
> >> board info is ether 60 or 72 bytes, so we get 2 or 3K table. Not above
> >> page, but still could be packed I think.
> >
> > Oh wow, that's impressively large.  Still not sure the optimization is
> > particularly worth it though, it's small change in the grand scheme of
> > things.  OTOH it's a small change.
> 
> Given this is done during early boot, what's the probability of not having
> sufficient contiguous memory?
> 
> >> If we decide that we want to keep single chunk I'll just change the
> >> allocation to kcalloc. Let me know.
> >
> > I'd be inclined to do that because it requires less thinking about the
> > value of what should be a very small optimization either way but
> > whatever :)
> 
> Tada...
> 
> commit f9bdb7fdd2cac17bdc9c344b6036e6939fa087cd
> Author: Markus Elfring <elfring@...rs.sourceforge.net>
> Date:   Fri Jan 13 12:28:04 2017 +0100
> 
>     spi: Use kcalloc() in spi_register_board_info()

Or even kmalloc_array() as zeroing out memory is not needed. But I'll
let Mark sort it out and drop my patch #2.

Thanks.

-- 
Dmitry