Re: [PATCH]: Cleanup of __alloc_pages

[Andrew Morton <akpm@osdl.org>]

"Rohit, Seth" <rohit.seth@intel.com> wrote:
>
> [PATCH]: Clean up of __alloc_pages. Couple of difference from original behavior:
> 	1- remove the initial reclaim logic
> 	2- GFP_HIGH pages are allowed to go little below watermark sooner.
> 	3- Search for free pages unconditionally after direct reclaim.

Would it be possible to break these into three separate patches?  The
cleanup part should be #1.

> +/* get_page_from_freeliest loops through all the possible zones
> + * to find out if it can allocate a page.  can_try_harder can have following
> + * values:
> + * -1 => No need to check for the watermarks.
> + *  0 => Don't go too low down in deeps below the low watermark (GFP_HIGH)
> + *  1 => Go far below the low watermark.  See zone_watermark_ok (RT TASK)
> + *
> + * cpuset check is not performed when the skip_cpuset_chk flag is set.
> + */
> +
> +static struct page *
> +get_page_from_freelist(gfp_t gfp_mask, unsigned int order, struct zone **zones, 
> +			int can_try_harder, int skip_cpuset_chk)
> +{
> +	struct zone *z;
> +	struct page *page = NULL;
> +	int classzone_idx = zone_idx(zones[0]);
> +	int i;
> +
> +	/*
> +	 * Go through the zonelist once, looking for a zone with enough free.
> +	 * See also cpuset_zone_allowed() comment in kernel/cpuset.c.
> +	 */
> +	for (i = 0; (z = zones[i]) != NULL; i++) {
> +		if (!skip_cpuset_chk && (!cpuset_zone_allowed(z, gfp_mask)))

It'd be nice to not have the `skip_cpuset_chk' flag there.  a) it gives
Linus conniptions and b) it's a little extra overhead for !CONFIG_CPUSETS
kernels.

> -	zone_statistics(zonelist, z);
> +	zone_statistics(zonelist, page_zone(page));

Evaluating page_zone() is not completely trivial.  Can we avoid the above?

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