On Fri, Sep 12, 2014 at 12:15:37AM +0200, Petr Tesarik wrote: > On Thu, 11 Sep 2014 17:16:37 -0400 > Vivek Goyal <vgoyal at redhat.com> wrote: > > > On Thu, Sep 11, 2014 at 10:43:30PM +0200, Petr Tesarik wrote: > > > On Thu, 11 Sep 2014 16:01:10 -0400 > > > Vivek Goyal <vgoyal at redhat.com> wrote: > > > > > > > On Fri, Sep 05, 2014 at 06:33:14PM +0200, Petr Tesarik wrote: > > > > > On architectures that use percpu-vm, the percpu region is not guaranteed > > > > > to be contiguous in physical space. > > > > > > > > Petr, > > > > > > > > Which are those arches? > > > > > > All except nommu. Actually, percpu-km will be used instead even on MMU > > > if SMP is disabled, but since SMP is pretty standard now, I guess the > > > vast majority of all kernels out there is affected. ;-) > > > > Hi Petr, > > > > To make sure I understand it correctly I will just summarize what you > > said. > > > > alloc_percpu() code does not guarantee that an object will be on physically > > contiguous pages if object crosses page boundary. That's why we are forcing > > allocation of object aligned to nearest higher power of two boundary of > > object size and that way object will always be on same page (as long as object > > is not bigger than a page). > > > > Is that a fair summary? > > Yes. I might add a note why physically contiguous memory is needed > here, but maybe it's obvious to anyone dealing with kdump. I think adding couple of lines to explain why physically contiguous notes are needed is a good idea. It will not be ovious to anybody new to kdump. Thanks Vivek
