From: Mike Kravetz <mike.kravetz@oracle.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>,
Joao Martins <joao.m.martins@oracle.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
John Hubbard <jhubbard@nvidia.com>,
Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH 2/2] mm/hugetlb: refactor subpage recording
Date: Sat, 13 Feb 2021 13:12:26 -0800 [thread overview]
Message-ID: <0b75d477-c041-7830-5d28-bdf0a3530ee9@oracle.com> (raw)
In-Reply-To: <20210127021023.GC4605@ziepe.ca>
On 1/26/21 6:10 PM, Jason Gunthorpe wrote:
> On Tue, Jan 26, 2021 at 05:58:53PM -0800, Mike Kravetz wrote:
>
>> As pointed out by Joao, you can also see the differences in pfn_to_page
>> for CONFIG_SPARSE_VMEMMAP and CONFIG_SPARSEMEM. The only time we might
>> have issues is with CONFIG_SPARSEMEM. I would bet CONFIG_SPARSE_VMEMMAP
>> is far more common.
>
> I think it is fine to have a different pfn_to_page, it should just be
> illegal to combine pages into a compound if their tail pages are not
> linear in the map.
>
> Matt's folio work might present an option to audit the whole mm for
> this pattern and provide some folio_next_tail_page() accessor that
> does the fast thing - but I question the value of such a project for a
> 2008 era PPC platform with 16GB pages (seriously?) that may be using
> VMEMMAP today anyhow??
>
> Maybe others know of more modern use cases
>
> Jason
When discussing v2 of this patch, Zi confirmed that this issue exists today.
See,
https://lore.kernel.org/linux-mm/3d2acb33-57e2-060d-616f-cce872c77307@oracle.com
I will fix up that unexpected discovery in the hugetlb code. But, not sure
what approach we want to take elsewhere, such as the GUP code.
--
Mike Kravetz
next prev parent reply other threads:[~2021-02-13 21:13 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-25 20:57 [PATCH 0/2] mm/hugetlb: follow_hugetlb_page() improvements Joao Martins
2021-01-25 20:57 ` [PATCH 1/2] mm/hugetlb: grab head page refcount once per group of subpages Joao Martins
2021-01-26 2:14 ` Mike Kravetz
2021-01-25 20:57 ` [PATCH 2/2] mm/hugetlb: refactor subpage recording Joao Martins
2021-01-26 18:08 ` Mike Kravetz
2021-01-26 19:21 ` Joao Martins
2021-01-26 19:24 ` Joao Martins
2021-01-26 21:21 ` Mike Kravetz
2021-01-26 23:20 ` Joao Martins
2021-01-27 0:07 ` Jason Gunthorpe
2021-01-27 1:58 ` Mike Kravetz
2021-01-27 2:10 ` Jason Gunthorpe
2021-02-13 21:12 ` Mike Kravetz [this message]
2021-01-27 2:24 ` Matthew Wilcox
2021-01-27 2:50 ` Zi Yan
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