Date: Thu, 14 May 2009 17:57:51 -0400 From: John Baldwin <jhb@freebsd.org> To: Ed Schouten <ed@80386.nl> Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org>, jt@0xabadba.be Subject: Re: concurrent sysctl implementation Message-ID: <200905141757.52144.jhb@freebsd.org> In-Reply-To: <20090514213426.GP58540@hoeg.nl> References: <a0806f900905050107u4cbf0624oc83aafa54ae651f0@mail.gmail.com> <200905111801.18767.jhb@freebsd.org> <20090514213426.GP58540@hoeg.nl>
next in thread | previous in thread | raw e-mail | index | archive | help
On Thursday 14 May 2009 5:34:26 pm Ed Schouten wrote: > * 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. Yes, I can commit it. -- John Baldwin
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200905141757.52144.jhb>