Apologies, just realised I should make a quick correction. When I said "The maxusers value gets compiled into the param.o object", I meant that values which are calculated from maxusers are compiled into the object file. MAXUSERS is a macro, and not itself placed into the object file.
On 4/30/17, Wiremu Demchick <william.demch...@gmail.com> wrote: > I'm new to the OpenBSD source, so I welcome correction from someone > who knows more. But, I'll put my neck out and attempt to give a basic > tour of this aspect of the source. > > The maxusers entry in the config(8) file is where it all begins. > http://man.openbsd.org/config.8 > > The figure of 80 seems to be the default used for GENERIC builds for > i386 and amd64. However, the figure is different for some platforms, > like Octeon, where it is 32. You may be interested in the following > source files: > sys/arch/amd64/conf/GENERIC > sys/arch/i386/conf/GENERIC > sys/arch/octeon/conf/GENERIC > > The maxusers value gets compiled into the param.o object, see: > sys/conf/param.c > sys/arch/amd64/conf/Makefile.amd64 lines 105-110 > > Note that in param.c the maxusers value is now called MAXUSERS. In > param.c, MAXUSERS is used to calculated a few values, namely > maxprocess, maxthread, maxfiles, and initialvnodes. > > Taking the example of maxprocess and maxthread, we see in > sys/kern/kern.c the following comment: > 287 /* > 288 * Although process entries are dynamically created, > we still keep > 289 * a global limit on the maximum number we will > create. We reserve > 290 * the last 5 processes to root. The variable nprocesses is > the > 291 * current number of processes, maxprocess is the > limit. Similar > 292 * rules for threads (struct proc): we reserve the > last 5 to root; > 293 * the variable nthreads is the current number of > procs, maxthread is > 294 * the limit. > 295 */ > > So, it would appear that in this case the maxprocess value (which is > calculated from MAXUSERS) is a global max. However, as far as I can > tell, it would appear that MAXUSERS is not an absolute limit on the > maximum number of users that can have processes running at a given > time, but is rather a variable used to estimate what resources are > required. (See again the config(8) manpage, which says maxusers is > "Used to size various system tables and maximum operating conditions > in an approximate fashion.".) > > Of course, there are the limits imposed upon individual users, but > that is a different mechanism. (See > http://man.openbsd.org/getrlimit.2, RLIMIT_NPROC. kern_fork.c also > implements this limit.) > > So, to answer your question, what happens when the process table is > full? Line 301 of kern_fork.c says: > return EAGAIN; > > That agrees with: > http://man.openbsd.org/fork.2 > > In the case of maxfiles, it seems like ENFILE is returned, but I have > not confirmed this: > http://man.openbsd.org/open.2 > > Mauri ora koutou. > > On 4/30/17, Luke Small <lukensm...@gmail.com> wrote: >> As I recall, there is a build configuration of 80 users for some kernel >> components. What happens if the system exceeds that number? >> > -- Wiremu Demchick īmēra - william.demch...@gmail.com īmēra - will...@generationzero.org.nz īmēra - william.demch...@enspiral.com waea - 04 282 0414 (+6442820414) waea pūkoro - 021 292 3891 (+64212923891) kei wikimedia - Kiwi128
