linux-kernel - Re: [PATCH] hugetlb: cond_resched for set_max_huge_pages and follow_hugetlb

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Date:	Fri, 24 Jul 2015 08:59:59 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Spencer Baugh <sbaugh@...ern.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	David Rientjes <rientjes@...gle.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Mike Kravetz <mike.kravetz@...cle.com>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	"open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
	open list <linux-kernel@...r.kernel.org>,
	Joern Engel <joern@...estorage.com>,
	Spencer Baugh <Spencer.baugh@...estorage.com>,
	Joern Engel <joern@...fs.org>
Subject: Re: [PATCH] hugetlb: cond_resched for set_max_huge_pages and
 follow_hugetlb_page

On Thu 23-07-15 14:54:31, Spencer Baugh wrote:
> From: Joern Engel <joern@...fs.org>
> 
> ~150ms scheduler latency for both observed in the wild.

This is way to vague. Could you describe your problem somehow more,
please?
There are schduling points in the page allocator (when it triggers the
reclaim), why are those not sufficient? Or do you manage to allocate
many hugetlb pages without performing the reclaim and that leads to
soft lockups?

> 
> Signed-off-by: Joern Engel <joern@...fs.org>
> Signed-off-by: Spencer Baugh <sbaugh@...ern.com>
> ---
>  mm/hugetlb.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index a8c3087..2eb6919 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1836,6 +1836,7 @@ static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count,
>  			ret = alloc_fresh_gigantic_page(h, nodes_allowed);
>  		else
>  			ret = alloc_fresh_huge_page(h, nodes_allowed);
> +		cond_resched();
>  		spin_lock(&hugetlb_lock);
>  		if (!ret)
>  			goto out;
> @@ -3521,6 +3522,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  				spin_unlock(ptl);
>  			ret = hugetlb_fault(mm, vma, vaddr,
>  				(flags & FOLL_WRITE) ? FAULT_FLAG_WRITE : 0);
> +			cond_resched();
>  			if (!(ret & VM_FAULT_ERROR))
>  				continue;
>  
> -- 
> 2.5.0.rc3
> 
> --
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-- 
Michal Hocko
SUSE Labs
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