linux-kernel - Re: [PATCH 04/10] hugetlb: hugepage migration core

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Date:	Fri, 3 Sep 2010 09:10:03 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
cc:	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Jun'ichi Nomura <j-nomura@...jp.nec.com>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/10] hugetlb: hugepage migration core

On Fri, 3 Sep 2010, Naoya Horiguchi wrote:

> diff --git v2.6.36-rc2/mm/vmscan.c v2.6.36-rc2/mm/vmscan.c
> index c391c32..69ce2a3 100644
> --- v2.6.36-rc2/mm/vmscan.c
> +++ v2.6.36-rc2/mm/vmscan.c
> @@ -40,6 +40,7 @@
>  #include <linux/memcontrol.h>
>  #include <linux/delayacct.h>
>  #include <linux/sysctl.h>
> +#include <linux/hugetlb.h>
>
>  #include <asm/tlbflush.h>
>  #include <asm/div64.h>
> @@ -508,6 +509,10 @@ void putback_lru_page(struct page *page)
>
>  	VM_BUG_ON(PageLRU(page));
>
> +	if (PageHuge(page)) {
> +		put_page(page);
> +		return;
> +	}
>  redo:
>  	ClearPageUnevictable(page);
>
> @@ -1112,7 +1117,9 @@ int isolate_lru_page(struct page *page)
>  {
>  	int ret = -EBUSY;
>
> -	if (PageLRU(page)) {
> +	if (PageHuge(page) && get_page_unless_zero(compound_head(page)))
> +		ret = 0;
> +	else if (PageLRU(page)) {
>  		struct zone *zone = page_zone(page);
>
>  		spin_lock_irq(&zone->lru_lock);
>

Huge pages are not on the LRU right? So why use the lru functions for
them and then not use the lru? Its a bit stranger. The caller must aware
of the different handling of huge pages since there is no toying around
with the lru. So just have the caller do a put or get page instead.

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