linux-kernel - Re: [PATCH v3 1/5] memblock: Introduce allocation direction to memblock.

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Date:	Mon, 23 Sep 2013 11:38:53 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Tang Chen <tangchen@...fujitsu.com>
Cc:	rjw@...k.pl, lenb@...nel.org, tglx@...utronix.de, mingo@...e.hu,
	hpa@...or.com, akpm@...ux-foundation.org, toshi.kani@...com,
	zhangyanfei@...fujitsu.com, liwanp@...ux.vnet.ibm.com,
	trenn@...e.de, yinghai@...nel.org, jiang.liu@...wei.com,
	wency@...fujitsu.com, laijs@...fujitsu.com,
	isimatu.yasuaki@...fujitsu.com, izumi.taku@...fujitsu.com,
	mgorman@...e.de, minchan@...nel.org, mina86@...a86.com,
	gong.chen@...ux.intel.com, vasilis.liaskovitis@...fitbricks.com,
	lwoodman@...hat.com, riel@...hat.com, jweiner@...hat.com,
	prarit@...hat.com, x86@...nel.org, linux-doc@...r.kernel.org,
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	linux-acpi@...r.kernel.org
Subject: Re: [PATCH v3 1/5] memblock: Introduce allocation direction to
 memblock.

Hello,

Sorry about the delay.  Was traveling.

On Fri, Sep 13, 2013 at 05:30:51PM +0800, Tang Chen wrote:
> +/* Allocation order. */
> +#define MEMBLOCK_DIRECTION_HIGH_TO_LOW	0
> +#define MEMBLOCK_DIRECTION_LOW_TO_HIGH	1
> +#define MEMBLOCK_DIRECTION_DEFAULT	MEMBLOCK_DIRECTION_HIGH_TO_LOW

Can we please settle on either top_down/bottom_up or
high_to_low/low_to_high?  The two seem to be used interchangeably in
the patch series.  Also, it'd be more customary to use enum for things
like above, but more on the interface below.

> +static inline bool memblock_direction_bottom_up(void)
> +{
> +	return memblock.current_direction == MEMBLOCK_DIRECTION_LOW_TO_HIGH;
> +}

Maybe just memblock_bottom_up() would be enough?

Also, why not also have memblock_set_bottom_up(bool enable) as the
'set' interface?

>  /**
> + * memblock_set_current_direction - Set current allocation direction to allow
> + *                                  allocating memory from higher to lower
> + *                                  address or from lower to higher address
> + *
> + * @direction: In which order to allocate memory. Could be
> + *             MEMBLOCK_DIRECTION_{HIGH_TO_LOW|LOW_TO_HIGH}
> + */
> +void memblock_set_current_direction(int direction);

Function comments should go with the function definition.  Dunno what
happened with set_current_limit but let's please not spread it.

> +void __init_memblock memblock_set_current_direction(int direction)
> +{
> +	if (direction != MEMBLOCK_DIRECTION_HIGH_TO_LOW &&
> +	    direction != MEMBLOCK_DIRECTION_LOW_TO_HIGH) {
> +		pr_warn("memblock: Failed to set allocation order. "
> +			"Invalid order type: %d\n", direction);
> +		return;
> +	}
> +
> +	memblock.current_direction = direction;
> +}

If set_bottom_up() style interface is used, the above will be a lot
simpler, right?  Also, it's kinda weird to have two separate patches
to introduce the flag and actually implement bottom up allocation.

Thanks.

-- 
tejun
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