Re: [Xen-devel] [PATCH for 2.3 v2 1/1] xen-hvm: increase maxmem before calling xc_domain_populate_physmap

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 3 Dec 2014, Don Slutz wrote:
> From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> 
> Increase maxmem before calling xc_domain_populate_physmap_exact to
> avoid the risk of running out of guest memory. This way we can also
> avoid complex memory calculations in libxl at domain construction
> time.
> 
> This patch fixes an abort() when assigning more than 4 NICs to a VM.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> Signed-off-by: Don Slutz <dslutz@xxxxxxxxxxx>
> ---
> v2: Changes by Don Slutz
>   Switch from xc_domain_getinfo to xc_domain_getinfolist
>   Fix error check for xc_domain_getinfolist
>   Limit increase of maxmem to only do when needed:
>     Add QEMU_SPARE_PAGES (How many pages to leave free)
>     Add free_pages calculation
> 
>  xen-hvm.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/xen-hvm.c b/xen-hvm.c
> index 7548794..d30e77e 100644
> --- a/xen-hvm.c
> +++ b/xen-hvm.c
> @@ -90,6 +90,7 @@ static inline ioreq_t *xen_vcpu_ioreq(shared_iopage_t 
> *shared_page, int vcpu)
>  #endif
>  
>  #define BUFFER_IO_MAX_DELAY  100
> +#define QEMU_SPARE_PAGES 16

We need a big comment here to explain why we have this parameter and
when we'll be able to get rid of it.

Other than that the patch is fine.

Thanks!


>  typedef struct XenPhysmap {
>      hwaddr start_addr;
> @@ -244,6 +245,8 @@ void xen_ram_alloc(ram_addr_t ram_addr, ram_addr_t size, 
> MemoryRegion *mr)
>      unsigned long nr_pfn;
>      xen_pfn_t *pfn_list;
>      int i;
> +    xc_domaininfo_t info;
> +    unsigned long free_pages;
>  
>      if (runstate_check(RUN_STATE_INMIGRATE)) {
>          /* RAM already populated in Xen */
> @@ -266,6 +269,22 @@ void xen_ram_alloc(ram_addr_t ram_addr, ram_addr_t size, 
> MemoryRegion *mr)
>          pfn_list[i] = (ram_addr >> TARGET_PAGE_BITS) + i;
>      }
>  
> +    if ((xc_domain_getinfolist(xen_xc, xen_domid, 1, &info) != 1) ||
> +        (info.domain != xen_domid)) {
> +        hw_error("xc_domain_getinfolist failed");
> +    }
> +    free_pages = info.max_pages - info.tot_pages;
> +    if (free_pages > QEMU_SPARE_PAGES) {
> +        free_pages -= QEMU_SPARE_PAGES;
> +    } else {
> +        free_pages = 0;
> +    }
> +    if ((free_pages < nr_pfn) &&
> +        (xc_domain_setmaxmem(xen_xc, xen_domid,
> +                             ((info.max_pages + nr_pfn - free_pages)
> +                              << (XC_PAGE_SHIFT - 10))) < 0)) {
> +        hw_error("xc_domain_setmaxmem failed");
> +    }
>      if (xc_domain_populate_physmap_exact(xen_xc, xen_domid, nr_pfn, 0, 0, 
> pfn_list)) {
>          hw_error("xen: failed to populate ram at " RAM_ADDR_FMT, ram_addr);
>      }
> -- 
> 1.8.4
> 

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