From: Matthew Wilcox <willy@infradead.org>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: linux-mm@kvack.org
Subject: Re: Splitting the mmap_sem
Date: Fri, 13 Dec 2019 06:33:33 -0800 [thread overview]
Message-ID: <20191213143333.GW32169@bombadil.infradead.org> (raw)
In-Reply-To: <20191212154613.qrfsqrgb24sj6fcx@box>
On Thu, Dec 12, 2019 at 06:46:13PM +0300, Kirill A. Shutemov wrote:
> On Thu, Dec 12, 2019 at 07:40:02AM -0800, Matthew Wilcox wrote:
> > On Thu, Dec 12, 2019 at 05:24:57PM +0300, Kirill A. Shutemov wrote:
> > > On Tue, Dec 03, 2019 at 02:21:47PM -0800, Matthew Wilcox wrote:
> > > > My preferred solution to the mmap_sem scalability problem is to allow
> > > > VMAs to be looked up under the RCU read lock then take a per-VMA lock.
> > > > I've been focusing on the first half of this problem (looking up VMAs
> > > > in an RCU-safe data structure) and ignoring the second half (taking a
> > > > lock while holding the RCU lock).
> > >
> > > Do you see this approach to be regression-free for uncontended case?
> > > I doubt it will not cause regressions for signle-threaded applications...
> >
> > Which part of the approach do you think will cause a regression? The
> > maple tree is quicker to traverse than the rbtree (in our simulations).
> > Incrementing a refcount on a VMA is surely no slower than acquiring an
> > uncontended rwsem for read. mmap() and munmap() will get slower, but is
> > that a problem?
>
> Yes, it does. Especially for short-living processes. See kernel build as a
> workload.
Ah. Well, we can skip the synchronize_rcu() step if the mm_struct has zero
or one mm_users. That should avoid a slowdown for mmap/munmap.
next prev parent reply other threads:[~2019-12-13 21:11 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 [this message]
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
2020-02-19 17:14 ` Laurent Dufour
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