On Tue, Mar 19, 2013 at 01:02:29PM -0700, Andrew Morton wrote: > On Sat, 16 Mar 2013 13:02:29 +0900 HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com> wrote: > > > If there's some vmcore object that doesn't satisfy page-size boundary > > requirement, remap_pfn_range() fails to remap it to user-space. > > > > Objects that posisbly don't satisfy the requirement are ELF note > > segments only. The memory chunks corresponding to PT_LOAD entries are > > guaranteed to satisfy page-size boundary requirement by the copy from > > old memory to buffer in 2nd kernel done in later patch. > > > > This patch doesn't copy each note segment into the 2nd kernel since > > they amount to so large in total if there are multiple CPUs. For > > example, current maximum number of CPUs in x86_64 is 5120, where note > > segments exceed 1MB with NT_PRSTATUS only. > > I don't really understand this. Why does the number of or size of > note segments affect their alignment? > > > --- a/fs/proc/vmcore.c > > +++ b/fs/proc/vmcore.c > > @@ -38,6 +38,8 @@ static u64 vmcore_size; > > > > static struct proc_dir_entry *proc_vmcore = NULL; > > > > +static bool support_mmap_vmcore; > > This is quite regrettable. It means that on some kernels/machines, > mmap(vmcore) simply won't work. This means that people might write > code which works for them, but which will fail for others when deployed > on a small number of machines. > > Can we avoid this? Why can't we just copy the notes even if there are > a large number of them? Actually initially he implemented copying notes to second kernel and I suggested to go other way (Tried too hard to save memory in second kernel). I guess it was not a good idea and copying notes keeps it simple. Thanks Vivek
