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

[Simon Jeons]

Hi Michal,
On 04/05/2013 05:30 PM, Michal Hocko wrote:
> On Fri 05-04-13 17:00:58, Simon Jeons wrote:
> > Hi Michal,
> > On 04/05/2013 04:08 PM, Michal Hocko wrote:
> > > On Fri 05-04-13 09:14:58, Simon Jeons wrote:
> > > > 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.
> > > because hugetlb_add_hstate creates hstate for those pages and
> > > hugetlb_init_hstates allocates them later on.
> > >
> > > > If there is no page table level to support them, how can
> > > > them present?
> > > Because hugetlb hstate handling code doesn't care about page tables and
> > > the way how those pages are going to be mapped _at all_. Or put it in
> > > another way. Nobody prevents you to allocate order-5 page for a single
> > > pte but that would be a pure waste. Page fault code expects that pages
> > > with a proper size are allocated.
> > Do you mean 32MB pages will map to one pmd which should map 2MB pages?
> Please refer to hugetlb_fault for more information.

Thanks for your pointing out. So my assume is correct, is it? Can pmd 
which support 2MB map 32MB pages work well?

>

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