From: Matthew Wilcox <willy@infradead.org>
To: James Houghton <jthoughton@google.com>
Cc: linux-mm@kvack.org, Vishal Moola <vishal.moola@gmail.com>,
Hugh Dickins <hughd@google.com>, Rik van Riel <riel@surriel.com>,
David Hildenbrand <david@redhat.com>,
"Yin, Fengwei" <fengwei.yin@intel.com>
Subject: Re: Folio mapcount
Date: Tue, 7 Feb 2023 23:35:54 +0000 [thread overview]
Message-ID: <Y+LgWgjD33pbM+A2@casper.infradead.org> (raw)
In-Reply-To: <CADrL8HVEenAmWHZRCmLkMAVD=g1jrimg+YEVhb953_Mwqi3OuQ@mail.gmail.com>
On Tue, Feb 07, 2023 at 03:27:07PM -0800, James Houghton wrote:
> So page_vma_mapped_walk() might have to walk up to HPAGE_PMD_NR-ish
> PTEs (if we find a bunch of pte_none() PTEs). Just curious, could that
> be any slower than what we currently do (like, incrementing up to
> HPAGE_PMD_NR-ish subpage mapcounts)? Or is it not a concern?
I think it's faster. Both of these operations work on folio_nr_pages()
entries ... but a page table is 8 bytes and a struct page is 64 bytes.
From a CPU prefetching point of view, they're both linear scans, but
PTEs are 8 times denser.
The other factor to consider is how often we do each of these operations.
Mapping a folio happens ~once per call to mmap() (even though it's delayed
until page fault time). Querying folio_total_mapcount() happens ... less
often, I think? Both are going to be quite rare since generally we map
the entire folio at once.
next prev parent reply other threads:[~2023-02-07 23:36 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-24 18:13 Matthew Wilcox
2023-01-24 18:35 ` David Hildenbrand
2023-01-24 18:37 ` David Hildenbrand
2023-01-24 18:35 ` Yang Shi
2023-02-02 3:45 ` Mike Kravetz
2023-02-02 15:31 ` Matthew Wilcox
2023-02-07 16:19 ` Zi Yan
2023-02-07 16:44 ` Matthew Wilcox
2023-02-06 20:34 ` Matthew Wilcox
2023-02-06 22:55 ` Yang Shi
2023-02-06 23:09 ` Matthew Wilcox
2023-02-07 3:06 ` Yin, Fengwei
2023-02-07 4:08 ` Matthew Wilcox
2023-02-07 22:39 ` Peter Xu
2023-02-07 23:27 ` Matthew Wilcox
2023-02-08 19:40 ` Peter Xu
2023-02-08 20:25 ` Matthew Wilcox
2023-02-08 20:58 ` Peter Xu
2023-02-09 15:10 ` Chih-En Lin
2023-02-09 15:43 ` Peter Xu
2023-02-07 22:56 ` James Houghton
2023-02-07 23:08 ` Matthew Wilcox
2023-02-07 23:27 ` James Houghton
2023-02-07 23:35 ` Matthew Wilcox [this message]
2023-02-08 0:35 ` James Houghton
2023-02-08 2:26 ` Matthew Wilcox
2023-02-07 16:23 ` Zi Yan
2023-02-07 16:51 ` Matthew Wilcox
2023-02-08 19:36 ` Zi Yan
2023-02-08 19:54 ` Matthew Wilcox
2023-02-10 15:15 ` Zi Yan
2023-03-29 14:02 ` Yin, Fengwei
2023-07-01 1:17 ` Zi Yan
2023-07-02 9:50 ` Yin, Fengwei
2023-07-02 11:45 ` David Hildenbrand
2023-07-02 12:26 ` Matthew Wilcox
2023-07-03 20:54 ` David Hildenbrand
2023-07-02 19:51 ` Zi Yan
2023-07-03 1:09 ` Yin, Fengwei
2023-07-03 13:24 ` Zi Yan
2023-07-03 20:46 ` David Hildenbrand
2023-07-04 1:22 ` Yin, Fengwei
2023-07-04 2:25 ` Matthew Wilcox
2023-07-03 21:09 ` David Hildenbrand
-- strict thread matches above, loose matches on Subject: below --
2021-12-15 21:55 folio mapcount Matthew Wilcox
2021-12-16 9:37 ` Kirill A. Shutemov
2021-12-16 13:56 ` Matthew Wilcox
2021-12-16 15:19 ` Jason Gunthorpe
2021-12-16 15:54 ` Matthew Wilcox
2021-12-16 16:45 ` David Hildenbrand
2021-12-16 17:01 ` Jason Gunthorpe
2021-12-16 18:56 ` Kirill A. Shutemov
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