Re: [RFC][PATCH 0/9] extend hugepage migration

[Simon Jeons]

Hi Michal,
On 03/22/2013 04:15 PM, Michal Hocko wrote:
> [getting off-list]
>
> On Fri 22-03-13 07:46:32, Simon Jeons wrote:
> > Hi Michal,
> > On 03/21/2013 08:56 PM, Michal Hocko wrote:
> > > On Thu 21-03-13 07:49:48, Simon Jeons wrote:
> > > [...]
> > > > When I hacking arch/x86/mm/hugetlbpage.c like this,
> > > > diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
> > > > index ae1aa71..87f34ee 100644
> > > > --- a/arch/x86/mm/hugetlbpage.c
> > > > +++ b/arch/x86/mm/hugetlbpage.c
> > > > @@ -354,14 +354,13 @@ hugetlb_get_unmapped_area(struct file *file,
> > > > unsigned long addr,
> > > >
> > > > #endif /*HAVE_ARCH_HUGETLB_UNMAPPED_AREA*/
> > > >
> > > > -#ifdef CONFIG_X86_64
> > > > static __init int setup_hugepagesz(char *opt)
> > > > {
> > > > unsigned long ps = memparse(opt, &opt);
> > > > if (ps == PMD_SIZE) {
> > > > hugetlb_add_hstate(PMD_SHIFT - PAGE_SHIFT);
> > > > - } else if (ps == PUD_SIZE && cpu_has_gbpages) {
> > > > - hugetlb_add_hstate(PUD_SHIFT - PAGE_SHIFT);
> > > > + } else if (ps == PUD_SIZE) {
> > > > + hugetlb_add_hstate(PMD_SHIFT - PAGE_SHIFT+4);
> > > > } else {
> > > > printk(KERN_ERR "hugepagesz: Unsupported page size %lu M\n",
> > > > ps >> 20);
> > > >
> > > > I set boot=hugepagesz=1G hugepages=10, then I got 10 32MB huge pages.
> > > > What's the difference between these pages which I hacking and normal
> > > > huge pages?
> > > How is this related to the patch set?
> > > Please _stop_ distracting discussion to unrelated topics!
> > >
> > > Nothing personal but this is just wasting our time.
> > Sorry kindly Michal, my bad.
> > Btw, could you explain this question for me? very sorry waste your time.
> Your CPU has to support GB pages. You have removed cpu_has_gbpages test
> and added a hstate for order 13 pages which is a weird number on its
> own (32MB) because there is no page table level to support them.

But after hacking, there is /sys/kernel/mm/hugepages/hugepages-*, and 
have equal number of 32MB huge pages which I set up in boot parameter. 
If there is no page table level to support them, how can them present? I 
can hacking this successfully in ubuntu, but not in fedora.


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