[EMAIL PROTECTED] wrote: > >> 1) because determining which pages are used exclusively by the process >> cannot be achieved by reading /proc/<pid>/map of a single process. As >> far as I can see one needs to read all /proc/<pid>/map files to be able >> to determine which objects are really shared. Additionally there is no >> way to differentiate between a file that is mmap'ed into this specific >> instance and a shared object that is mmap'ed into multiple process spaces. > > And how would the kernel know that a particular page is not shared? > > The VM system just can't tell in many cases whether there's still > sharing going on or not. > > - The library mappings are possibly shared copy-on-write > - The library BSS is not shared > - The stacks are not shared > - The heap is not shared > - Shared memory may be shared or not > - Read-only mappings can be shared or not. > >> 2) reading all /proc/<pid>/map files is slow and CPU intensive. > > that's because the kernel has to compute a bunch of things and you have > to compute them too; having them appear in psinfo would make creating > psinfo likely much more expensive. > > The problem of 'pages exclusively used' by a single process is a > relatively hard problem to solve. > > It's also not something that is easily kept by the kernel: > > - the first process to map a library would need to account for its > use > - the second process using it would cause the first process > exclusive use count to drop > - the last-but-one process exiting would cause the last process' > count to go up > > - is it fair to account all the resident pages in a library which > have been broagh in by process A to be accounted toward process B > after A has exited? > > > I think we need a clearer definition of the problem and whether we, given > the constraints of the current VM system, can actually achieve knowing this > metric; and if not, what alternative metric we do want. And whether we > want the new VM system to do such accounting properly. > > Casper >
Thank you Casper for clearing up the degree of impact of this. I agree that an implementation doing a precise accounting of exclusively used pages in kernel is not worth the effort. I will take a look what possibilities are left in user space to get an estimation of the amount of shared and exclusively used memory, because I still think this could be a helpful metric. Tom _______________________________________________ opensolaris-discuss mailing list opensolaris-discuss@opensolaris.org
