linux-kernel - Re: [PATCH 00/22] Add and use pci_zalloc

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Message-ID: <CAGRGNgVD2f0S-v8YZ-qABEhDJAwk5pp71FU9uLR8aSZ+DhABjg@mail.gmail.com>
Date:	Tue, 24 Jun 2014 09:27:25 +1000
From:	Julian Calaby <julian.calaby@...il.com>
To:	Joe Perches <joe@...ches.com>
Cc:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	linux-arch@...r.kernel.org,
	linux-scsi <linux-scsi@...r.kernel.org>, iss_storagedev@...com,
	linux-rdma@...r.kernel.org, netdev <netdev@...r.kernel.org>,
	linux-atm-general@...ts.sourceforge.net,
	linux-wireless <linux-wireless@...r.kernel.org>,
	dri-devel@...ts.freedesktop.org, linux-crypto@...r.kernel.org,
	linux-eata@...onnect.net, linux-media@...r.kernel.org
Subject: Re: [PATCH 00/22] Add and use pci_zalloc_consistent

Hi Joe,

On Tue, Jun 24, 2014 at 5:13 AM, Joe Perches <joe@...ches.com> wrote:
> On Mon, 2014-06-23 at 10:25 -0700, Luis R. Rodriguez wrote:
>> On Mon, Jun 23, 2014 at 06:41:28AM -0700, Joe Perches wrote:
>> > Adding the helper reduces object code size as well as overall
>> > source size line count.
>> >
>> > It's also consistent with all the various zalloc mechanisms
>> > in the kernel.
>> >
>> > Done with a simple cocci script and some typing.
>>
>> Awesome, any chance you can paste in the SmPL? Also any chance
>> we can get this added to a make coccicheck so that maintainers
>> moving forward can use that to ensure that no new code is
>> added that uses the old school API?
>
> Not many of these are recent.
>
> Arnd Bergmann reasonably suggested that the pci_alloc_consistent
> api be converted the the more widely used dma_alloc_coherent.
>
> https://lkml.org/lkml/2014/6/23/513
>
>> Shouldn't these drivers just use the normal dma-mapping API now?
>
> and I replied:
>
> https://lkml.org/lkml/2014/6/23/525
>
>> Maybe.  I wouldn't mind.
>> They do seem to have a trivial bit of unnecessary overhead for
>> hwdev == NULL ? NULL : &hwdev->dev
>
> Anyway, here's the little script.
> I'm not sure it's worthwhile to add it though.
>
> $ cat ./scripts/coccinelle/api/alloc/pci_zalloc_consistent.cocci
> ///
> /// Use pci_zalloc_consistent rather than
> ///     pci_alloc_consistent followed by memset with 0
> ///
> /// This considers some simple cases that are common and easy to validate
> /// Note in particular that there are no ...s in the rule, so all of the
> /// matched code has to be contiguous
> ///
> /// Blatantly cribbed from: scripts/coccinelle/api/alloc/kzalloc-simple.cocci
>
> @@
> type T, T2;
> expression x;
> expression E1,E2,E3;
> statement S;
> @@
>
> - x = (T)pci_alloc_consistent(E1,E2,E3);
> + x = pci_zalloc_consistent(E1,E2,E3);
>   if ((x==NULL) || ...) S
> - memset((T2)x,0,E2);

I don't know much about SmPL, but wouldn't having that if statement
there reduce your matches?

Thanks,

-- 
Julian Calaby

Email: julian.calaby@...il.com
Profile: http://www.google.com/profiles/julian.calaby/
.Plan: http://sites.google.com/site/juliancalaby/
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