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From: Jason Gunthorpe <jgg@ziepe.ca>
To: Mike Kravetz <mike.kravetz@oracle.com>
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: Tue, 26 Jan 2021 22:10:23 -0400	[thread overview]
Message-ID: <20210127021023.GC4605@ziepe.ca> (raw)
In-Reply-To: <f1fc1543-72fa-44f2-50fc-0220abfdc484@oracle.com>

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

  reply	other threads:[~2021-01-27  4:05 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 [this message]
2021-02-13 21:12               ` Mike Kravetz
2021-01-27  2:24           ` Matthew Wilcox
2021-01-27  2:50             ` Zi Yan

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