Michal, Am 05.01.2017 um 11:53 schrieb Michal Hocko: > I guess you meant s@overflow@underflow@ right?
Yep, of course. > On Thu 05-01-17 00:29:18, Richard Weinberger wrote: >> /proc/<pid>/status can report extremely high VmLib values which >> will confuse monitoring tools. >> VmLib is mm->exec_vm minus text size, where exec_vm is the number of >> bytes backed by an executable memory mapping and text size is >> mm->end_code - mm->start_code as set up by binfmt. >> >> For the vast majority of all programs text size is smaller than exec_vm. >> But if a program interprets binaries on its own the calculation result >> can be negative. >> UserModeLinux is such an example. It installs and removes lots of PROT_EXEC >> mappings but mm->start_code and mm->start_code remain and VmLib turns >> negative. >> >> Fix this by detecting the overflow and just return 0. >> For interpreting the value reported by VmLib is anyway useless but >> returning 0 does at least not confuse userspace. > > Is really 0 what the userspace expects? Why shouldn't we just report > exec_vm unconditionally? Btw. we used to do something that many years > back https://lkml.org/lkml/2004/8/24/47. We are exporting the text size > so the calculation can be done by the userspace. Strictly speaking both values, 0 and exec_vm are wrong. Userspace expects VmLib to be 0 when an application has no libs loaded, i.e. for statically linked binaries. So, either we report 0 as "I don't know" or exec_vm, which is also wrong. I thought 0 is the better choice since it will not lead to wrong results when userspace tools compute the sum of values reported by /proc/<pid>/status. Thanks, //richard
