Re: [Xen-devel] [PATCH v2 1/1] xen: move TLB-flush filtering out into populate_physmap

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 06/09/16 09:42, Dongli Zhang wrote:
> This patch implemented parts of TODO left in commit id
> a902c12ee45fc9389eb8fe54eeddaf267a555c58. It moved TLB-flush filtering out
> into populate_physmap.
> 
> Because of TLB-flush in alloc_heap_pages, it's very slow to create a guest
> with memory size of more than 100GB on host with 100+ cpus.
> 
> This patch introduced a "MEMF_no_tlbflush" bit to memflag to indicate
> whether TLB-flush should be done in alloc_heap_pages or its caller
> populate_physmap.  Once this bit is set in memflag, alloc_heap_pages will
> ignore TLB-flush.

This makes pages accessible to the guest B, when guest A may still have
a cached mapping to them.

I think it is only safe to do this when guest B is being constructed.

David

> Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
> ---
>  xen/common/memory.c     | 26 ++++++++++++++++++++++++++
>  xen/common/page_alloc.c |  3 ++-
>  xen/include/xen/mm.h    |  2 ++
>  3 files changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/common/memory.c b/xen/common/memory.c
> index f34dd56..50c1a07 100644
> --- a/xen/common/memory.c
> +++ b/xen/common/memory.c
> @@ -141,6 +141,8 @@ static void populate_physmap(struct memop_args *a)
>      unsigned int i, j;
>      xen_pfn_t gpfn, mfn;
>      struct domain *d = a->domain, *curr_d = current->domain;
> +    bool_t need_tlbflush = 0;
> +    uint32_t tlbflush_timestamp = 0;
>  
>      if ( !guest_handle_subrange_okay(a->extent_list, a->nr_done,
>                                       a->nr_extents-1) )
> @@ -150,6 +152,8 @@ static void populate_physmap(struct memop_args *a)
>                              max_order(curr_d)) )
>          return;
>  
> +    a->memflags |= MEMF_no_tlbflush;
> +
>      for ( i = a->nr_done; i < a->nr_extents; i++ )
>      {
>          if ( i != a->nr_done && hypercall_preempt_check() )
> @@ -214,6 +218,18 @@ static void populate_physmap(struct memop_args *a)
>                      goto out;
>                  }
>  
> +                for ( j = 0; j < (1U << a->extent_order); j++ )
> +                {
> +                    if ( page[j].u.free.need_tlbflush &&
> +                         (page[j].tlbflush_timestamp <= 
> tlbflush_current_time()) &&
> +                         (!need_tlbflush ||
> +                         (page[j].tlbflush_timestamp > tlbflush_timestamp)) )
> +                    {
> +                        need_tlbflush = 1;
> +                        tlbflush_timestamp = page[j].tlbflush_timestamp;
> +                    }
> +                }
> +
>                  mfn = page_to_mfn(page);
>              }
>  
> @@ -232,6 +248,16 @@ static void populate_physmap(struct memop_args *a)
>      }
>  
>  out:
> +    if ( need_tlbflush )
> +    {
> +        cpumask_t mask = cpu_online_map;
> +        tlbflush_filter(mask, tlbflush_timestamp);
> +        if ( !cpumask_empty(&mask) )
> +        {
> +            perfc_incr(need_flush_tlb_flush);
> +            flush_tlb_mask(&mask);
> +        }
> +    }
>      a->nr_done = i;
>  }
>  
> diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
> index 18ff6cf..e0283fc 100644
> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -827,7 +827,8 @@ static struct page_info *alloc_heap_pages(
>          BUG_ON(pg[i].count_info != PGC_state_free);
>          pg[i].count_info = PGC_state_inuse;
>  
> -        if ( pg[i].u.free.need_tlbflush &&
> +        if ( !(memflags & MEMF_no_tlbflush) &&
> +             pg[i].u.free.need_tlbflush &&
>               (pg[i].tlbflush_timestamp <= tlbflush_current_time()) &&
>               (!need_tlbflush ||
>                (pg[i].tlbflush_timestamp > tlbflush_timestamp)) )
> diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
> index 58bc0b8..880ca88 100644
> --- a/xen/include/xen/mm.h
> +++ b/xen/include/xen/mm.h
> @@ -221,6 +221,8 @@ struct npfec {
>  #define  MEMF_exact_node  (1U<<_MEMF_exact_node)
>  #define _MEMF_no_owner    5
>  #define  MEMF_no_owner    (1U<<_MEMF_no_owner)
> +#define _MEMF_no_tlbflush 6
> +#define  MEMF_no_tlbflush (1U<<_MEMF_no_tlbflush)
>  #define _MEMF_node        8
>  #define  MEMF_node_mask   ((1U << (8 * sizeof(nodeid_t))) - 1)
>  #define  MEMF_node(n)     ((((n) + 1) & MEMF_node_mask) << _MEMF_node)
> 


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