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From: Mike Kravetz <mike.kravetz@oracle.com>
To: Jason Gunthorpe <jgg@ziepe.ca>, Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Zi Yan <ziy@nvidia.com>, Davidlohr Bueso <dbueso@suse.de>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Oscar Salvador <osalvador@suse.de>,
	Joao Martins <joao.m.martins@oracle.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH 1/2] hugetlb: fix update_and_free_page contig page struct assumption
Date: Thu, 18 Feb 2021 09:34:41 -0800	[thread overview]
Message-ID: <cc94992a-0eff-bf5e-d904-b23d5facfca3@oracle.com> (raw)
In-Reply-To: <20210218172500.GA4718@ziepe.ca>

On 2/18/21 9:25 AM, Jason Gunthorpe wrote:
> On Thu, Feb 18, 2021 at 02:45:54PM +0000, Matthew Wilcox wrote:
>> On Wed, Feb 17, 2021 at 11:02:52AM -0800, Andrew Morton wrote:
>>> On Wed, 17 Feb 2021 10:49:25 -0800 Mike Kravetz <mike.kravetz@oracle.com> wrote:
>>>> page structs are not guaranteed to be contiguous for gigantic pages.  The
>>>
>>> June 2014.  That's a long lurk time for a bug.  I wonder if some later
>>> commit revealed it.
>>
>> I would suggest that gigantic pages have not seen much use.  Certainly
>> performance with Intel CPUs on benchmarks that I've been involved with
>> showed lower performance with 1GB pages than with 2MB pages until quite
>> recently.
> 
> I suggested in another thread that maybe it is time to consider
> dropping this "feature"
> 
> If it has been slightly broken for 7 years it seems a good bet it
> isn't actually being used.
> 
> The cost to fix GUP to be compatible with this will hurt normal
> GUP performance - and again, that nobody has hit this bug in GUP
> further suggests the feature isn't used..

I was thinking that we could detect these 'unusual' configurations and only
do the slower page struct walking in those cases.  However, we would need to
do some research to make sure we have taken into account all possible config
options which can produce non-contiguous page structs.  That should have zero
performance impact in the 'normal' cases.

I suppose we could prohibit gigantic pages in these 'unusual' configurations.
It would require some research to see if this 'may' impact someone.
-- 
Mike Kravetz

  parent reply	other threads:[~2021-02-18 19:08 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-17 18:49 [PATCH 1/2] hugetlb: fix update_and_free_page contig page struct assumption Mike Kravetz
2021-02-17 18:49 ` [PATCH 2/2] hugetlb: fix copy_huge_page_from_user " Mike Kravetz
2021-02-17 19:02 ` [PATCH 1/2] hugetlb: fix update_and_free_page " Andrew Morton
2021-02-17 19:38   ` Mike Kravetz
2021-02-18 14:45   ` Matthew Wilcox
2021-02-18 17:25     ` Jason Gunthorpe
2021-02-18 17:27       ` Zi Yan
2021-02-18 17:32         ` Jason Gunthorpe
2021-02-18 17:40           ` Zi Yan
2021-02-18 17:51             ` Mike Kravetz
2021-02-18 18:50               ` Zi Yan
2021-02-18 17:34       ` Mike Kravetz [this message]
2021-02-18 21:43         ` Mike Kravetz

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