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From: David Laight <David.Laight@ACULAB.COM>
To: 'Eric Dumazet' <eric.dumazet@gmail.com>,
	Nate Karstens <nate.karstens@garmin.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	"Jeff Layton" <jlayton@kernel.org>,
	"J. Bruce Fields" <bfields@fieldses.org>,
	"Arnd Bergmann" <arnd@arndb.de>,
	Richard Henderson <rth@twiddle.net>,
	"Ivan Kokshaysky" <ink@jurassic.park.msu.ru>,
	Matt Turner <mattst88@gmail.com>,
	"James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>,
	Helge Deller <deller@gmx.de>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	"linux-alpha@vger.kernel.org" <linux-alpha@vger.kernel.org>,
	"linux-parisc@vger.kernel.org" <linux-parisc@vger.kernel.org>,
	"sparclinux@vger.kernel.org" <sparclinux@vger.kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc: Changli Gao <xiaosuo@gmail.com>
Subject: RE: [PATCH 1/4] fs: Implement close-on-fork
Date: Wed, 22 Apr 2020 08:35:23 +0000
Message-ID: <39a872f23b16405fb4e4683bf049beef@AcuMS.aculab.com> (raw)
In-Reply-To: <36dce9b4-a0bf-0015-f6bc-1006938545b1@gmail.com>

From: Eric Dumazet
> Sent: 20 April 2020 11:26
> On 4/20/20 12:15 AM, Nate Karstens wrote:
> > The close-on-fork flag causes the file descriptor to be closed
> > atomically in the child process before the child process returns
> > from fork(). Implement this feature and provide a method to
> > get/set the close-on-fork flag using fcntl(2).
> >
> > This functionality was approved by the Austin Common Standards
> > Revision Group for inclusion in the next revision of the POSIX
> > standard (see issue 1318 in the Austin Group Defect Tracker).
> 
> Oh well... yet another feature slowing down a critical path.
...
> I suggest we group the two bits of a file (close_on_exec, close_on_fork) together,
> so that we do not have to dirty two separate cache lines.
> 
> Otherwise we will add yet another cache line miss at every file opening/closing for processes
> with big file tables.

How about only allocating the 'close on fork' bitmap the first time
a process sets a bit in it?

Off hand I can't imagine the use case.
I thought posix always shared fd tables across fork().

	David

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  parent reply index

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-20  7:15 Nate Karstens
2020-04-20  7:15 ` [PATCH 1/4] fs: " Nate Karstens
2020-04-20 10:25   ` Eric Dumazet
2020-04-22  3:38     ` Changli Gao
2020-04-22  3:41       ` Changli Gao
2020-04-22  8:35     ` David Laight [this message]
2020-05-01 14:45     ` Karstens, Nate
2020-05-01 15:23       ` Matthew Wilcox
2020-05-03 13:52       ` David Laight
2020-04-22 15:36   ` Karstens, Nate
2020-04-22 15:43     ` Matthew Wilcox
2020-04-22 16:02       ` Karstens, Nate
2020-04-22 16:31         ` Bernd Petrovitsch
2020-04-22 16:55           ` David Laight
2020-04-23 12:34             ` Bernd Petrovitsch
2020-04-20  7:15 ` [PATCH 2/4] fs: Add O_CLOFORK flag for open(2) and dup3(2) Nate Karstens
2020-04-20  7:15 ` [PATCH 3/4] fs: Add F_DUPFD_CLOFORK to fcntl(2) Nate Karstens
2020-04-20  7:15 ` [PATCH 4/4] net: Add SOCK_CLOFORK Nate Karstens
2020-04-22 14:32 ` Implement close-on-fork James Bottomley
2020-04-22 15:01 ` Al Viro
2020-04-22 15:18   ` Matthew Wilcox
2020-04-22 15:34     ` James Bottomley
2020-04-22 16:00     ` Al Viro
2020-04-22 16:13       ` Al Viro
2020-05-04 13:46       ` Karstens, Nate

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