[Xen-devel] Re: [Linux PATCH] Mark hugepages to the hypervisor to speed up mapping (with signoff this time)

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 06/09/2010 10:20 AM, Dave McCracken wrote:
> Two new hypercalls were recently added to the Xen hypervisor to mark
> and unmark hugepages as in use.  Once a hugepage has been marked,
> actually mapping the hugepage is sped up by a significant amount (more
> than 20 times faster).
>
> This patch marks hugepages when they are added to the hugepage pool
> and unmarks them when they are removed.  It also checks to make sure
> each hugepage is contiguous at the machine level.
>
> Signed-off-by: Dave McCracken <dave.mccracken@xxxxxxxxxx>
>
> --------
>
>
> --- next/arch/x86/xen/mmu.c   2010-06-01 11:41:54.000000000 -0500
> +++ next-fh//arch/x86/xen/mmu.c       2010-06-02 08:45:01.000000000 -0500
> @@ -2531,3 +2531,51 @@ static int __init xen_mmu_debugfs(void)
>  fs_initcall(xen_mmu_debugfs);
>  
>  #endif       /* CONFIG_XEN_DEBUG_FS */
> +
> +static int mark_ok = 1;
>   

__read_mostly

> +
> +int arch_prepare_hugepage(struct page *page)
> +{
> +     struct mmuext_op op;
> +     unsigned long pfn, mfn, m;
> +     int i;
> +     int rc;
> +
> +     pfn = page_to_pfn(page);
> +     mfn = pfn_to_mfn(pfn);
> +     if (mfn & ((HPAGE_SIZE/PAGE_SIZE)-1)) {
> +             printk("Guest pages are not properly aligned to use 
> hugepages\n");
>   

Don't use printk to do this.  Use WARN() to print a stack trace so you
can work out who's doing this.

> +             return 1;
> +     }
> +     for (i = 0, m = mfn; i < HPAGE_SIZE/PAGE_SIZE; i++, pfn++, m++) {
> +             if (pfn_to_mfn(pfn) != m) {
> +                     printk("Guest pages are not properly aligned to use 
> hugepages\n");
>   
Isn't this a superset of the previous test?

> +                     return 1;
> +             }
> +     }
> +     /* It's ok if this fails.  We just fall back to the slow refcounting */
> +     if (mark_ok) {
> +             op.cmd = MMUEXT_MARK_SUPER;
> +             op.arg1.mfn = mfn;
> +             rc = HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF);
> +             if (rc) {
> +                     if (rc == -ENOSYS) {
> +                             mark_ok = 0;
> +                             return 0;
> +                     }
> +                     return 1;
> +             }
> +     }
> +     return 0;
> +}
> +
> +void arch_release_hugepage(struct page *page)
> +{
> +     struct mmuext_op op;
> +
> +     if (mark_ok) {
> +             op.cmd = MMUEXT_UNMARK_SUPER;
> +             op.arg1.mfn = pfn_to_mfn(page_to_pfn(page));
> +             HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF);
> +     }
> +}
> --- next/arch/x86/include/asm/hugetlb.h       2010-06-01 11:41:54.000000000 
> -0500
> +++ next-fh//arch/x86/include/asm/hugetlb.h   2010-06-02 08:37:58.000000000 
> -0500
> @@ -95,6 +95,10 @@ static inline int huge_ptep_set_access_f
>       return changed;
>  }
>  
> +#ifdef CONFIG_XEN
> +int arch_prepare_hugepage(struct page *page);
> +void arch_release_hugepage(struct page *page);
> +#else
>  static inline int arch_prepare_hugepage(struct page *page)
>  {
>       return 0;
> @@ -103,5 +107,6 @@ static inline int arch_prepare_hugepage(
>  static inline void arch_release_hugepage(struct page *page)
>  {
>  }
> +#endif
>   

That won't work.  What if you boot a CONFIG_XEN kernel native?

Something like:

#ifdef CONFIG_XEN
int xen_prepare_hugepage(struct page *page);
#else
static inline int xen_prepare_hugepage(struct page *page)
{
        return 0;
}
#endif

static inline int arch_prepare_hugepage(struct page *page)
{
        if (xen_pv_domain())
                return xen_prepare_hugepage(page);
        return 0;
}

might work better.

    J

>  
>  #endif /* _ASM_X86_HUGETLB_H */
> --- next/include/xen/interface/xen.h  2010-06-01 11:41:59.000000000 -0500
> +++ next-fh//include/xen/interface/xen.h      2010-06-02 08:38:50.000000000 
> -0500
> @@ -167,6 +167,19 @@
>   * cmd: MMUEXT_SET_LDT
>   * linear_addr: Linear address of LDT base (NB. must be page-aligned).
>   * nr_ents: Number of entries in LDT.
> + *
> + * cmd: MMUEXT_CLEAR_PAGE
> + * mfn: Machine frame number to be cleared.
> + *
> + * cmd: MMUEXT_COPY_PAGE
> + * mfn: Machine frame number of the destination page.
> + * src_mfn: Machine frame number of the source page.
> + *
> + * cmd: MMUEXT_MARK_SUPER
> + * mfn: Machine frame number of head of superpage to be marked.
> + *
> + * cmd: MMUEXT_UNMARK_SUPER
> + * mfn: Machine frame number of head of superpage to be cleared.
>   */
>  #define MMUEXT_PIN_L1_TABLE      0
>  #define MMUEXT_PIN_L2_TABLE      1
> @@ -183,6 +196,10 @@
>  #define MMUEXT_FLUSH_CACHE      12
>  #define MMUEXT_SET_LDT          13
>  #define MMUEXT_NEW_USER_BASEPTR 15
> +#define MMUEXT_CLEAR_PAGE       16
> +#define MMUEXT_COPY_PAGE        17
> +#define MMUEXT_MARK_SUPER       19
> +#define MMUEXT_UNMARK_SUPER     20
>  
>  #ifndef __ASSEMBLY__
>  #include <linux/types.h>
>
>   


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