linux-kernel - Re: [PATCH 01/22] pci-dma-compat: Add pci_zalloc

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Message-Id: <20140625122755.152685fadbc9cffe7a298dc6@linux-foundation.org>
Date:	Wed, 25 Jun 2014 12:27:55 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Joe Perches <joe@...ches.com>
Cc:	linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH 01/22] pci-dma-compat: Add pci_zalloc_consistent helper

On Mon, 23 Jun 2014 06:41:29 -0700 Joe Perches <joe@...ches.com> wrote:

> Add this helper for consistency with pci_zalloc_coherent
> and the ability to remove unnecessary memset(,0,) uses.

While we're being anal..  I'm not a big fan of the patch titles.  Worst
is "amd: Use pci_zalloc_consistent".  "amd" is quite a poor identifier
- it's only when you get in and look at the diff that you realise it's
an ethernet driver.

People sometimes address this by using

	"drivers: net: ethernet: amd: use pci_zalloc_consistent"

which strikes me as utterly perverse.  We already have a nice way of
representing the hierarchy and that's using '/'.

So when the irritation gets too high and when I can be bothered I'll
rewrite things like that to

	"drivers/net/ethernet/amd: use pci_zalloc_consistent"

which strikes me as being blindingly obvious, but apparently I'm in a
small minority :(

> --- a/include/asm-generic/pci-dma-compat.h
> +++ b/include/asm-generic/pci-dma-compat.h
> @@ -19,6 +19,14 @@ pci_alloc_consistent(struct pci_dev *hwdev, size_t size,
>  	return dma_alloc_coherent(hwdev == NULL ? NULL : &hwdev->dev, size, dma_handle, GFP_ATOMIC);
>  }
>  
> +static inline void *
> +pci_zalloc_consistent(struct pci_dev *hwdev, size_t size,
> +		      dma_addr_t *dma_handle)
> +{
> +	return dma_zalloc_coherent(hwdev == NULL ? NULL : &hwdev->dev,
> +				   size, dma_handle, GFP_ATOMIC);
> +}
> +

We'd get a smaller kernel by uninlining this.  It is hardly
performance-sensitive.  Uninlining would presumably use more stack,
but GFP_ATOMIC won't use a ton of stack anyway.

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