Date: Thu, 14 May 2009 23:34:26 +0200 From: Ed Schouten <ed@80386.nl> To: John Baldwin <jhb@freebsd.org> Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org>, jt@0xabadba.be Subject: Re: concurrent sysctl implementation Message-ID: <20090514213426.GP58540@hoeg.nl> In-Reply-To: <200905111801.18767.jhb@freebsd.org> References: <a0806f900905050107u4cbf0624oc83aafa54ae651f0@mail.gmail.com> <200905111224.26856.jhb@freebsd.org> <a0806f900905111127p378628bbw89e1d45f087e558e@mail.gmail.com> <200905111801.18767.jhb@freebsd.org>
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[-- Attachment #1 --] * John Baldwin <jhb@freebsd.org> wrote: > Well, in theory a bunch of "small" requests to SYSCTL_PROC() nodes that used > sysctl_wire_old() (or whatever it is called) could cause the amount of user > memory wired for sysctls to grow unbounded. Thus, allowing this limited > concurrency is a tradeoff as there is a minimal (perhaps only theoretical at > the moment) risk of removing the safety net. > > The patch is quite small, btw, because the locking for the sysctl tree already > exists, and by using read locks, one can already allow concurrent sysctl > requests. There is no need to add any new locks or restructure the sysctl > tree, just to adjust the locking that is already present. It might be > clearer, in fact, to split the sysctl memory lock back out into a separate > lock. This would allow "small" sysctl requests to run concurrently with a > single "large" request whereas in my suggestion in the earlier e-mail, > the "large" request will block all other user requests until it finishes. > > I've actually gone ahead and done this below. Boohoo. I actually wanted jt to work on this, as a small exercise to figure out the way locking primitives work in the kernel. No problem, because I can think of dozens of other things. Is there a chance we can see this patch in 8.0? I like it that the memlock is being picked up before we pick up the sysctl lock itself, which makes a lot of sense. -- Ed Schouten <ed@80386.nl> WWW: http://80386.nl/ [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (FreeBSD) iEYEARECAAYFAkoMjmIACgkQ52SDGA2eCwW0hACbB/4W3DshwsRPIuaXta+Wl8IX Y34An1UveDTp8oQMQb8jOCiMAgaTk2ve =vX/X -----END PGP SIGNATURE-----
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