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Howlett" , "Dave Hansen" , "Greg Kroah-Hartman" , "Guenter Roeck" , "Jann Horn" , "Jonathan Corbet" , "Jorge Lucangeli Obes" , "Matthew Wilcox" , "Muhammad Usama Anjum" , =?utf-8?q?Stephen_R=C3=B6ttger?= , "Suren Baghdasaryan" , "Amer Al Shanawany" , "Javier Carrasco" , "Shuah Khan" , , , , , Subject: Re: [linus:master] [mseal] 8be7258aad: stress-ng.pagemove.page_remaps_per_sec -4.4% regression From: "Nicholas Piggin" To: "Linus Torvalds" , "Jeff Xu" X-Mailer: aerc 0.18.2 References: <202408041602.caa0372-oliver.sang@intel.com> In-Reply-To: On Tue Aug 6, 2024 at 5:48 AM AEST, Linus Torvalds wrote: > On Mon, 5 Aug 2024 at 12:38, Jeff Xu wrote: > > > > I'm curious, why does ppc need to unmap vdso ? ( other archs don't > > have unmap logic.) > > I have no idea. There are comments about 'perf' getting confused about > mmap counts when 'context.vdso' isn't set up. > > But x86 has the same context.vdso logic, and does *not* set the > pointer before installing the vma, for example. Also does not zero it > out on munmap(), although it does have the mremap logic. > > For all I know it may all be entirely unnecessary, and could be > removed entirely. I don't know much about vdso code, it predated my involvedment in ppc. Commit 83d3f0e90c6c8 says CRIU (checkpoint restore in userspace) is moving it around. Why CRIU wants to do that, I don't know. Can userspace on other archs not unmap their vdsos? Thanks, Nick