Re: [Xen-devel] [BISECTED] Linux 3.12.7 introduces page map handling regression

[Mel Gorman <mgorman@xxxxxxx>]

On Thu, Jan 23, 2014 at 11:23:37AM -0500, Elena Ufimtseva wrote:
> >> >> <SNIP>
> >> >>
> >> >> This dump doesn't look dramatically different, either.
> >> >>
> >> >>>
> >> >>> The other question is - how is AutoNUMA running when it is not enabled?
> >> >>> Shouldn't those _PAGE_NUMA ops be nops when AutoNUMA hasn't even been
> >> >>> turned on?
> >> >>
> >> >>
> >> >> Well, NUMA_BALANCING is enabled in the kernel config[1], but I presume 
> >> >> you
> >> >> mean not enabled at runtime?
> >> >>
> >> >> [1]
> >> >> http://git.uplinklabs.net/snoonan/projects/archlinux/ec2/ec2-packages.git/tree/linux-ec2/config.x86_64
> >>
> >>
> >>
> >> --
> >> Elena
> 
> I was able to reproduce this consistently, also with the latest mm
> patches from yesterday.
> Can you please try this:
> 

Thanks Elena,

> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index ce563be..76dcf96 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -365,7 +365,7 @@ void xen_ptep_modify_prot_commit(struct mm_struct
> *mm, unsigned long addr,
>  /* Assume pteval_t is equivalent to all the other *val_t types. */
>  static pteval_t pte_mfn_to_pfn(pteval_t val)
>  {
> -       if (val & _PAGE_PRESENT) {
> +       if ((val & _PAGE_PRESENT) || ((val &
> (_PAGE_NUMA|_PAGE_PRESENT)) == _PAGE_NUMA)) {
>                 unsigned long mfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
>                 unsigned long pfn = mfn_to_pfn(mfn);
> 
> @@ -381,7 +381,7 @@ static pteval_t pte_mfn_to_pfn(pteval_t val)
> 
>  static pteval_t pte_pfn_to_mfn(pteval_t val)
>  {
> -       if (val & _PAGE_PRESENT) {
> +       if ((val & _PAGE_PRESENT) || ((val &
> (_PAGE_NUMA|_PAGE_PRESENT)) == _PAGE_NUMA)) {
>                 unsigned long pfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
>                 pteval_t flags = val & PTE_FLAGS_MASK;
>                 unsigned long mfn;

Would reusing pte_present be an option? Ordinarily I expect that
PAGE_NUMA/PAGE_PROTNONE is only set if PAGE_PRESENT is not set and pte_present
is defined as

static inline int pte_present(pte_t a)
{
        return pte_flags(a) & (_PAGE_PRESENT | _PAGE_PROTNONE |
                               _PAGE_NUMA);
}

So it looks like it work work. Of course it would need to be split to
reuse it within xen if pte_present was split to have a pteval_present
helper like so

static inline int pteval_present(pteval_t val)
{
        /*
         * Yes Linus, _PAGE_PROTNONE == _PAGE_NUMA. Expressing it this
         * way clearly states that the intent is that a protnone and numa
         * hinting ptes are considered present for the purposes of
         * pagetable operations like zapping, protection changes, gup etc.
         */
        return val & (_PAGE_PRESENT | _PAGE_PROTNONE | _PAGE_NUMA);
}

static inline int pte_present(pte_t pte)
{
        return pteval_present(pte_flags(pte))
}

If Xen is doing some other tricks with _PAGE_PRESENT then it might be
ruled out as an option. If so, then maybe it could still be made a
little clearer for future reference?


diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index c1d406f..ff621de 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -365,7 +365,7 @@ void xen_ptep_modify_prot_commit(struct mm_struct *mm, 
unsigned long addr,
 /* Assume pteval_t is equivalent to all the other *val_t types. */
 static pteval_t pte_mfn_to_pfn(pteval_t val)
 {
-       if (val & _PAGE_PRESENT) {
+       if ((val & _PAGE_PRESENT) || pteval_numa(val)) {
                unsigned long mfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
                unsigned long pfn = mfn_to_pfn(mfn);
 
@@ -381,7 +381,7 @@ static pteval_t pte_mfn_to_pfn(pteval_t val)
 
 static pteval_t pte_pfn_to_mfn(pteval_t val)
 {
-       if (val & _PAGE_PRESENT) {
+       if ((val & _PAGE_PRESENT) || pteval_numa(val)) {
                unsigned long pfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
                pteval_t flags = val & PTE_FLAGS_MASK;
                unsigned long mfn;
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 8e4f41d..693fe00 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -654,10 +654,14 @@ static inline int pmd_trans_unstable(pmd_t *pmd)
  * (because _PAGE_PRESENT is not set).
  */
 #ifndef pte_numa
+static inline int pteval_numa(pteval_t pteval)
+{
+       return (pteval & (_PAGE_NUMA|_PAGE_PRESENT)) == _PAGE_NUMA;
+}
+
 static inline int pte_numa(pte_t pte)
 {
-       return (pte_flags(pte) &
-               (_PAGE_NUMA|_PAGE_PRESENT)) == _PAGE_NUMA;
+       return pteval_numa(pte_flags(pte));
 }
 #endif
 

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