linux-kernel - Re: [RFC PATCH 1/5] mm, page_alloc: support multiple pages allocation

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Message-ID: <51DDE5BA.9020800@intel.com>
Date:	Wed, 10 Jul 2013 15:52:42 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Glauber Costa <glommer@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Minchan Kim <minchan@...nel.org>,
	Jiang Liu <jiang.liu@...wei.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Joonsoo Kim <js1304@...il.com>
Subject: Re: [RFC PATCH 1/5] mm, page_alloc: support multiple pages allocation

On 07/03/2013 01:34 AM, Joonsoo Kim wrote:
> -		if (page)
> +		do {
> +			page = buffered_rmqueue(preferred_zone, zone, order,
> +							gfp_mask, migratetype);
> +			if (!page)
> +				break;
> +
> +			if (!nr_pages) {
> +				count++;
> +				break;
> +			}
> +
> +			pages[count++] = page;
> +			if (count >= *nr_pages)
> +				break;
> +
> +			mark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
> +			if (!zone_watermark_ok(zone, order, mark,
> +					classzone_idx, alloc_flags))
> +				break;
> +		} while (1);

I'm really surprised this works as well as it does.  Calling
buffered_rmqueue() a bunch of times enables/disables interrupts a bunch
of times, and mucks with the percpu pages lists a whole bunch.
buffered_rmqueue() is really meant for _single_ pages, not to be called
a bunch of times in a row.

Why not just do a single rmqueue_bulk() call?
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