linux-kernel - Re: [PATCH] Allow compaction of unevictable pages

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Date:	Fri, 6 Mar 2015 13:07:02 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Eric B Munson <emunson@...mai.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Lameter <cl@...ux.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Allow compaction of unevictable pages

On Fri, 6 Mar 2015, Eric B Munson wrote:

> diff --git a/mm/compaction.c b/mm/compaction.c
> index 8c0d945..33c81e1 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1056,7 +1056,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
>  {
>  	unsigned long low_pfn, end_pfn;
>  	struct page *page;
> -	const isolate_mode_t isolate_mode =
> +	const isolate_mode_t isolate_mode = ISOLATE_UNEVICTABLE |
>  		(cc->mode == MIGRATE_ASYNC ? ISOLATE_ASYNC_MIGRATE : 0);
>  
>  	/*

I agree that memory compaction should be isolating and migrating 
unevictable memory for better results, and we have been running with a 
similar patch internally for about a year for the same purpose as you, 
higher probability of allocating hugepages.

This would be better off removing the notion of ISOLATE_UNEVICTABLE 
entirely, however, since CMA and now memory compaction would be using it, 
so the check in __isolate_lru_page() is no longer necessary.  Has the 
added bonus of removing about 10 lines of soure code.
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