linux-kernel - Re: [PATCH -V4 08/10] hugetlbfs: Add a list for tracking in-use HugeTLB pages

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Message-ID: <20120328135845.GH20949@tiehlicka.suse.cz>
Date:	Wed, 28 Mar 2012 15:58:46 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	linux-mm@...ck.org, mgorman@...e.de,
	kamezawa.hiroyu@...fujitsu.com, dhillf@...il.com,
	aarcange@...hat.com, akpm@...ux-foundation.org, hannes@...xchg.org,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH -V4 08/10] hugetlbfs: Add a list for tracking in-use
 HugeTLB pages

On Fri 16-03-12 23:09:28, Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
> 
> hugepage_activelist will be used to track currently used HugeTLB pages.
> We need to find the in-use HugeTLB pages to support memcg removal.
> On memcg removal we update the page's memory cgroup to point to
> parent cgroup.
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> ---
>  include/linux/hugetlb.h |    1 +
>  mm/hugetlb.c            |   23 ++++++++++++++++++-----
>  2 files changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index cbd8dc5..6919100 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
[...]
> @@ -2319,14 +2322,24 @@ void __unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
>  		page = pte_page(pte);
>  		if (pte_dirty(pte))
>  			set_page_dirty(page);
> -		list_add(&page->lru, &page_list);
> +
> +		spin_lock(&hugetlb_lock);
> +		list_move(&page->lru, &page_list);
> +		spin_unlock(&hugetlb_lock);

Why do we really need the spinlock here?

>  	}
>  	spin_unlock(&mm->page_table_lock);
>  	flush_tlb_range(vma, start, end);
>  	mmu_notifier_invalidate_range_end(mm, start, end);
>  	list_for_each_entry_safe(page, tmp, &page_list, lru) {
>  		page_remove_rmap(page);
> -		list_del(&page->lru);
> +		/*
> +		 * We need to move it back huge page active list. If we are
> +		 * holding the last reference, below put_page will move it
> +		 * back to free list.
> +		 */
> +		spin_lock(&hugetlb_lock);
> +		list_move(&page->lru, &h->hugepage_activelist);
> +		spin_unlock(&hugetlb_lock);

This spinlock usage doesn't look nice but I guess we do not have many
other options.

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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