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From: Zi Yan <ziy@nvidia.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Roman Gushchin <guro@fb.com>, <linux-mm@kvack.org>,
	Rik van Riel <riel@surriel.com>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Matthew Wilcox <willy@infradead.org>,
	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 11:09:25 -0400	[thread overview]
Message-ID: <3CDAD67E-23A1-4D84-BF19-FFE1CF956779@nvidia.com> (raw)
In-Reply-To: <20200907072014.GD30144@dhcp22.suse.cz>

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On 7 Sep 2020, at 3:20, Michal Hocko wrote:

> On Fri 04-09-20 14:10:45, Roman Gushchin wrote:
>> On Fri, Sep 04, 2020 at 09:42:07AM +0200, Michal Hocko wrote:
> [...]
>>> An explicit opt-in sounds much more appropriate to me as well. If we go
>>> with a specific API then I would not make it 1GB pages specific. Why
>>> cannot we have an explicit interface to "defragment" address space
>>> range into large pages and the kernel would use large pages where
>>> appropriate? Or is the additional copying prohibitively expensive?
>>
>> Can you, please, elaborate a bit more here? It seems like madvise(MADV_HUGEPAGE)
>> provides something similar to what you're describing, but there are lot
>> of details here, so I'm probably missing something.
>
> MADV_HUGEPAGE is controlling a preference for THP to be used for a
> particular address range. So it looks similar but the historical
> behavior is to control page faults as well and the behavior depends on
> the global setup.
>
> I've had in mind something much simpler. Effectively an API to invoke
> khugepaged (like) functionality synchronously from the calling context
> on the specific address range. It could be more aggressive than the
> regular khugepaged and create even 1G pages (or as large THPs as page
> tables can handle on the particular arch for that matter).
>
> As this would be an explicit call we do not have to be worried about
> the resulting latency because it would be an explicit call by the
> userspace.  The default khugepaged has a harder position there because
> has no understanding of the target address space and cannot make any
> cost/benefit evaluation so it has to be more conservative.

Something like MADV_HUGEPAGE_SYNC? It would be useful, since users have
better and clearer control of getting huge pages from the kernel and
know when they will pay the cost of getting the huge pages.

I would think the suggestion is more about the huge page control options
currently provided by the kernel do not have predictable performance
outcome, since MADV_HUGEPAGE is a best-effort option and does not tell
users whether the marked virtual address range is backed by huge pages
or not when the madvise returns. MADV_HUGEPAGE_SYNC would provide a
deterministic result to users on whether the huge page(s) are formed
or not.

—
Best Regards,
Yan Zi

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  reply	other threads:[~2020-09-08 20:16 UTC|newest]

Thread overview: 85+ 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 [this message]
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
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 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 13:49                     ` 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 13:32                       ` Rik van Riel
2020-09-10 14:30                       ` Zi Yan
2020-09-09 13:59                 ` Michal Hocko

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