From: Matthew Wilcox <willy@infradead.org>
To: Zi Yan <ziy@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>,
Roman Gushchin <guro@fb.com>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
linux-mm@kvack.org, Rik van Riel <riel@surriel.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Shakeel Butt <shakeelb@google.com>,
Yang Shi <yang.shi@linux.alibaba.com>,
David Nellans <dnellans@nvidia.com>,
linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 00/16] 1GB THP support on x86_64
Date: Tue, 8 Sep 2020 15:27:58 +0100 [thread overview]
Message-ID: <20200908142758.GF27537@casper.infradead.org> (raw)
In-Reply-To: <7E20392E-5ED7-4C22-9555-F3BAABF3CBE9@nvidia.com>
On Tue, Sep 08, 2020 at 10:05:11AM -0400, Zi Yan wrote:
> On 8 Sep 2020, at 7:57, David Hildenbrand wrote:
> > I have concerns if we would silently use 1~GB THPs in most scenarios
> > where be would have used 2~MB THP. I'd appreciate a trigger to
> > explicitly enable that - MADV_HUGEPAGE is not sufficient because some
> > applications relying on that assume that the THP size will be 2~MB
> > (especially, if you want sparse, large VMAs).
>
> This patchset is not intended to silently use 1GB THP in place of 2MB THP.
> First of all, there is a knob /sys/kernel/mm/transparent_hugepage/enable_1GB
> to enable 1GB THP explicitly. Also, 1GB THP is allocated from a reserved CMA
> region (although I had alloc_contig_pages as a fallback, which can be removed
> in next version), so users need to add hugepage_cma=nG kernel parameter to
> enable 1GB THP allocation. If a finer control is necessary, we can add
> a new MADV_HUGEPAGE_1GB for 1GB THP.
I think we do need that flag. Machines don't run a single workload
(arguably with VMs, we're getting closer to going back to the single
workload per machine, but that's a different matter). So if there's
one app that wants 2MB pages and one that wants 1GB pages, we need to
be able to distinguish them.
I could also see there being an app which benefits from 1GB for
one mapping and prefers 2GB for a different mapping, so I think the
per-mapping madvise flag is best.
I'm a little wary of encoding the size of an x86 PUD in the Linux API
though. Probably best to follow the example set in
include/uapi/asm-generic/hugetlb_encode.h, but I don't love it. I
don't have a better suggestion though.
next prev parent reply other threads:[~2020-09-08 14:30 UTC|newest]
Thread overview: 82+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-02 18:06 [RFC PATCH 00/16] 1GB THP support on x86_64 Zi Yan
2020-09-02 18:06 ` [RFC PATCH 01/16] mm: add pagechain container for storing multiple pages Zi Yan
2020-09-02 20:29 ` Randy Dunlap
2020-09-02 20:48 ` Zi Yan
2020-09-03 3:15 ` Matthew Wilcox
2020-09-07 12:22 ` Kirill A. Shutemov
2020-09-07 15:11 ` Zi Yan
2020-09-09 13:46 ` Kirill A. Shutemov
2020-09-09 14:15 ` Zi Yan
2020-09-02 18:06 ` [RFC PATCH 02/16] mm: thp: 1GB anonymous page implementation Zi Yan
2020-09-02 18:06 ` [RFC PATCH 03/16] mm: proc: add 1GB THP kpageflag Zi Yan
2020-09-09 13:46 ` Kirill A. Shutemov
2020-09-02 18:06 ` [RFC PATCH 04/16] mm: thp: 1GB THP copy on write implementation Zi Yan
2020-09-02 18:06 ` [RFC PATCH 05/16] mm: thp: handling 1GB THP reference bit Zi Yan
2020-09-09 14:09 ` Kirill A. Shutemov
2020-09-09 14:36 ` Zi Yan
2020-09-02 18:06 ` [RFC PATCH 06/16] mm: thp: add 1GB THP split_huge_pud_page() function Zi Yan
2020-09-09 14:18 ` Kirill A. Shutemov
2020-09-09 14:19 ` Zi Yan
2020-09-02 18:06 ` [RFC PATCH 07/16] mm: stats: make smap stats understand PUD THPs Zi Yan
2020-09-02 18:06 ` [RFC PATCH 08/16] mm: page_vma_walk: teach it about PMD-mapped PUD THP Zi Yan
2020-09-02 18:06 ` [RFC PATCH 09/16] mm: thp: 1GB THP support in try_to_unmap() Zi Yan
2020-09-02 18:06 ` [RFC PATCH 10/16] mm: thp: split 1GB THPs at page reclaim Zi Yan
2020-09-02 18:06 ` [RFC PATCH 11/16] mm: thp: 1GB THP follow_p*d_page() support Zi Yan
2020-09-02 18:06 ` [RFC PATCH 12/16] mm: support 1GB THP pagemap support Zi Yan
2020-09-02 18:06 ` [RFC PATCH 13/16] mm: thp: add a knob to enable/disable 1GB THPs Zi Yan
2020-09-02 18:06 ` [RFC PATCH 14/16] mm: page_alloc: >=MAX_ORDER pages allocation an deallocation Zi Yan
2020-09-02 18:06 ` [RFC PATCH 15/16] hugetlb: cma: move cma reserve function to cma.c Zi Yan
2020-09-02 18:06 ` [RFC PATCH 16/16] mm: thp: use cma reservation for pud thp allocation Zi Yan
2020-09-02 18:40 ` [RFC PATCH 00/16] 1GB THP support on x86_64 Jason Gunthorpe
2020-09-02 18:45 ` Zi Yan
2020-09-02 18:48 ` Jason Gunthorpe
2020-09-02 19:05 ` Zi Yan
2020-09-02 19:57 ` Jason Gunthorpe
2020-09-02 20:29 ` Zi Yan
2020-09-03 16:40 ` Jason Gunthorpe
2020-09-03 16:55 ` Matthew Wilcox
2020-09-03 17:08 ` Jason Gunthorpe
2020-09-03 7:32 ` Michal Hocko
2020-09-03 16:25 ` Roman Gushchin
2020-09-03 16:50 ` Jason Gunthorpe
2020-09-03 17:01 ` Matthew Wilcox
2020-09-03 17:18 ` Jason Gunthorpe
2020-09-03 20:57 ` Mike Kravetz
2020-09-03 21:06 ` Roman Gushchin
2020-09-04 7:42 ` Michal Hocko
2020-09-04 21:10 ` Roman Gushchin
2020-09-07 7:20 ` Michal Hocko
2020-09-08 15:09 ` Zi Yan
2020-09-08 19:58 ` Roman Gushchin
2020-09-09 4:01 ` John Hubbard
2020-09-09 7:15 ` Michal Hocko
2020-09-03 14:23 ` Kirill A. Shutemov
2020-09-03 16:30 ` Roman Gushchin
2020-09-08 11:57 ` David Hildenbrand
2020-09-08 14:05 ` Zi Yan
2020-09-08 14:22 ` David Hildenbrand
2020-09-08 15:36 ` Zi Yan
2020-09-08 14:27 ` Matthew Wilcox [this message]
2020-09-08 15:50 ` Zi Yan
2020-09-09 12:11 ` Jason Gunthorpe
2020-09-09 12:32 ` Matthew Wilcox
2020-09-09 13:14 ` Jason Gunthorpe
2020-09-09 13:27 ` David Hildenbrand
2020-09-10 10:02 ` William Kucharski
2020-09-08 14:35 ` Michal Hocko
2020-09-08 14:41 ` Rik van Riel
2020-09-08 15:02 ` David Hildenbrand
2020-09-09 7:04 ` Michal Hocko
2020-09-09 13:19 ` Rik van Riel
2020-09-09 13:43 ` David Hildenbrand
2020-09-09 13:49 ` Rik van Riel
2020-09-09 13:54 ` David Hildenbrand
2020-09-10 7:32 ` Michal Hocko
2020-09-10 8:27 ` David Hildenbrand
2020-09-10 14:21 ` Zi Yan
2020-09-10 14:34 ` David Hildenbrand
2020-09-10 14:41 ` Zi Yan
2020-09-10 15:15 ` David Hildenbrand
2020-09-10 13:32 ` Rik van Riel
2020-09-10 14:30 ` Zi Yan
2020-09-09 13:59 ` Michal Hocko
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