From: Weijie Yang <weijie.yang.kh@gmail.com>
To: Michal Nazarewicz <mina86@mina86.com>
Cc: Gregory Fong <gregory.0xf0@gmail.com>,
linux-mm@kvack.org, Laura Abbott <lauraa@codeaurora.org>,
iamjoonsoo.kim@lge.com,
Marek Szyprowski <m.szyprowski@samsung.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Florian Fainelli <f.fainelli@gmail.com>,
Brian Norris <computersforpeace@gmail.com>
Subject: Re: CMA alignment question
Date: Thu, 6 Nov 2014 09:00:33 +0800 [thread overview]
Message-ID: <CAL1ERfMk+rhd=-MaLC2VVj61-T17_SVgKL4=Z_okhEYktFJ+tQ@mail.gmail.com> (raw)
In-Reply-To: <xa1tsihxwblf.fsf@mina86.com>
On Thu, Nov 6, 2014 at 6:01 AM, Michal Nazarewicz <mina86@mina86.com> wrote:
>> On Tue, Nov 04 2014, Gregory Fong wrote:
>>> The alignment in cma_alloc() is done w.r.t. the bitmap. This is a
>>> problem when, for example:
>>>
>>> - a device requires 16M (order 12) alignment
>>> - the CMA region is not 16 M aligned
>
> On Wed, Nov 05 2014, Weijie Yang wrote:
>> I think the device driver should ensure that situation could not occur,
>> by assign suitable alignment parameter in cma_declare_contiguous().
>
> What about default CMA area? Besides, I think principle of least
> surprise applies here and alignment should be physical.
I agree the current code doesn't handle this issue properly.
However, I prefer to add specific usage to CMA interface rather than
modify the cma code, Because the latter hide the issue and could waste
memory.
> --
> Best regards, _ _
> .o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o
> ..o | Computer Science, Michał “mina86” Nazarewicz (o o)
> ooo +--<mpn@google.com>--<xmpp:mina86@jabber.org>--ooO--(_)--Ooo--
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next prev parent reply other threads:[~2014-11-06 1:00 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-04 21:03 Gregory Fong
2014-11-04 22:27 ` Michal Nazarewicz
2014-11-05 4:18 ` Gregory Fong
2014-11-05 7:20 ` Weijie Yang
2014-11-05 22:01 ` Michal Nazarewicz
2014-11-06 1:00 ` Weijie Yang [this message]
2014-11-06 12:29 ` Michal Nazarewicz
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