linux-kernel - Re: [PATCH] hugetlbfs: Kill applications that use MAP_NORESERVE with SIGBUS instead of OOM-killer

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Date:	Tue, 20 Apr 2010 16:33:07 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Lee Schermerhorn <lee.schermerhorn@...com>,
	David Rientjes <rientjes@...gle.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] hugetlbfs: Kill applications that use MAP_NORESERVE
 with SIGBUS instead of OOM-killer

On Tue, 20 Apr 2010 18:44:07 +0100
Mel Gorman <mel@....ul.ie> wrote:

> Ordinarily, application using hugetlbfs will create mappings with
> reserves. For shared mappings, these pages are reserved before mmap()
> returns success and for private mappings, the caller process is
> guaranteed and a child process that cannot get the pages gets killed
> with sigbus.
> 
> An application that uses MAP_NORESERVE gets no reservations and mmap()
> will always succeed at the risk the page will not be available at fault
> time. This might be used for example on very large sparse mappings where the
> developer is confident the necessary huge pages exist to satisfy all faults
> even though the whole mapping cannot be backed by huge pages.  Unfortunately,
> if an allocation does fail, VM_FAULT_OOM is returned to the fault handler
> which proceeds to trigger the OOM-killer. This is unhelpful.
> 
> This patch alters hugetlbfs to kill a process that uses MAP_NORESERVE
> where huge pages were not available with SIGBUS instead of triggering
> the OOM killer.
> 
> This patch if accepted should also be considered a -stable candidate.

Why?  The changelog doesn't convey much seriousness?

> Signed-off-by: Mel Gorman <mel@....ul.ie>
> ---
>  mm/hugetlb.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 6034dc9..af2d907 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1038,7 +1038,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
>  		page = alloc_buddy_huge_page(h, vma, addr);
>  		if (!page) {
>  			hugetlb_put_quota(inode->i_mapping, chg);
> -			return ERR_PTR(-VM_FAULT_OOM);
> +			return ERR_PTR(-VM_FAULT_SIGBUS);
>  		}
>  	}
>  

This affects hugetlb_cow() as well?


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