linux-kernel - Re: [PATCH] mm, hugetlb: gimme back my page

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Message-ID: <52EA57AC.3090700@oracle.com>
Date:	Thu, 30 Jan 2014 08:46:20 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Davidlohr Bueso <davidlohr@...com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Jonathan Gonzalez <jgonzalez@...ets.cl>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm, hugetlb: gimme back my page

On 01/30/2014 01:37 AM, Davidlohr Bueso wrote:
> From: Davidlohr Bueso<davidlohr@...com>
>
> While testing some changes, I noticed an issue triggered by the libhugetlbfs
> test-suite. This is caused by commit 309381fe (mm: dump page when hitting a
> VM_BUG_ON using VM_BUG_ON_PAGE), where an application can unexpectedly OOM due
> to another program that using, or reserving, pool_size-1 pages later triggers
> a VM_BUG_ON_PAGE and thus greedly leaves no memory to the rest of the hugetlb
> aware tasks. For example, in libhugetlbfs 2.14:
>
> mmap-gettest 10 32783 (2M: 64): <---- hit VM_BUG_ON_PAGE
> mmap-cow 32782 32783 (2M: 32):  FAIL    Failed to create shared mapping: Cannot allocate memory
> mmap-cow 32782 32783 (2M: 64):  FAIL    Failed to create shared mapping: Cannot allocate memory
>
> While I have not looked into why 'mmap-gettest' keeps failing, it is of no
> importance to this particular issue. This problem is similar to why we have
> the hugetlb_instantiation_mutex, hugepages are quite finite.
>
> Revert the use of VM_BUG_ON_PAGE back to just VM_BUG_ON.

VM_BUG_ON_PAGE is just a VM_BUG_ON that does dump_page before the BUG().

The only reason to use VM_BUG_ON instead of VM_BUG_ON_PAGE is if the page you're working
with doesn't make sense/isn't useful as debug output.

If doing a dump_page is causing issues somewhere then dump_pages should be fixed - instead
of hiding the problem under the rug by not using it.


Thanks,
sasha
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