From: Matthew Wilcox <willy@infradead.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: SeongJae Park <sj38.park@gmail.com>,
Michal Hocko <mhocko@suse.com>, Vlastimil Babka <vbabka@suse.cz>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
linux-mm@kvack.org
Subject: Re: Re: Splitting the mmap_sem
Date: Mon, 10 Feb 2020 14:00:42 -0800 [thread overview]
Message-ID: <20200210220042.GN8731@bombadil.infradead.org> (raw)
In-Reply-To: <20200207085234.GB14914@hirez.programming.kicks-ass.net>
On Fri, Feb 07, 2020 at 09:52:34AM +0100, Peter Zijlstra wrote:
> On Thu, Feb 06, 2020 at 01:20:24PM -0800, Matthew Wilcox wrote:
> > If you use SRCU, why would you need a second page table walk?
>
> Because SRCU only ensures the VMA object remains extant, it does not
> prevent modification of it, normally that guarantee is provided by
> mmap_sem, but we're not going to use that.
>
> Instead, what we serialize on is the (split) ptlock. So we do the first
> page-walk and ptlock to verify the vma-lookup, then we drop ptlock and
> do the file-io, then we page-walk and take ptlock again, verify the vma
> (again) and install the PTE. If anything goes wrong, we bail.
>
> See this patch:
>
> https://lkml.kernel.org/r/301fb863785f37c319b493bd0d43167353871804.1479465699.git.ldufour@linux.vnet.ibm.com
OK, this gets to a difference in how we see modification to a VMA working.
You take a seqcount in patch 5:
https://lore.kernel.org/linux-mm/95790e53bfcfb536eb8f1dcdf4750e7e8050d8f4.1479465699.git.ldufour@linux.vnet.ibm.com/
I was intending to postpone the page table flushing parts of a VMA
modification until a grace period had passed, but what you're doing
is faster.
next prev parent reply other threads:[~2020-02-10 22:00 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-03 22:21 Splitting the mmap_sem Matthew Wilcox
2019-12-05 17:21 ` Jerome Glisse
2019-12-06 5:13 ` Matthew Wilcox
2019-12-06 17:30 ` Jerome Glisse
2019-12-09 3:33 ` Matthew Wilcox
2019-12-09 14:17 ` Jerome Glisse
2019-12-10 15:26 ` Vlastimil Babka
2019-12-10 16:07 ` Jerome Glisse
2019-12-10 18:09 ` Vlastimil Babka
2019-12-12 14:24 ` Kirill A. Shutemov
2019-12-12 15:40 ` Matthew Wilcox
2019-12-12 15:46 ` Kirill A. Shutemov
2019-12-13 14:33 ` Matthew Wilcox
2019-12-13 18:06 ` Kirill A. Shutemov
2019-12-13 18:21 ` Matthew Wilcox
2020-01-06 22:09 ` Matthew Wilcox
2020-01-07 12:34 ` Kirill A. Shutemov
2020-01-07 13:54 ` Matthew Wilcox
2020-01-07 14:27 ` Kirill A. Shutemov
2020-01-09 13:56 ` Vlastimil Babka
2020-01-09 17:03 ` Michal Hocko
2020-01-09 17:07 ` Michal Hocko
2020-01-09 17:32 ` SeongJae Park
2020-01-09 20:13 ` Matthew Wilcox
2020-02-06 13:59 ` Peter Zijlstra
2020-02-06 20:15 ` Matthew Wilcox
2020-02-06 20:55 ` Peter Zijlstra
2020-02-06 21:20 ` Matthew Wilcox
2020-02-07 8:52 ` Peter Zijlstra
2020-02-10 22:00 ` Matthew Wilcox [this message]
2020-02-19 17:14 ` Laurent Dufour
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