Re: [Qemu-devel] [PATCH 2/2] migration/postcopy: Explicitly disallow huge pages

[Daniel P. Berrange]

On Thu, Sep 29, 2016 at 08:09:38PM +0100, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
> 
> At the moment postcopy will fail as soon as qemu tries to register
> userfault on the RAMBlock pages that are backed by hugepages.
> However, the kernel is going to get userfault support for hugepage
> at some point, and we've not got the rest of the QEMU code to support
> it yet, so fail neatly with an error like:
> 
> Postcopy doesn't support hugetlbfs yet (/objects/mem1)
> 
> Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> ---
>  migration/postcopy-ram.c | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
> 
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index 9b04778..9723593 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -85,6 +85,23 @@ static bool ufd_version_check(int ufd)
>  }
>  
>  /*
> + * Check for things that postcopy won't support; returns 0 if the block
> + * is fine.
> + */
> +static int check_range(const char *block_name, void *host_addr,
> +                      ram_addr_t offset, ram_addr_t length, void *opaque)
> +{
> +    RAMBlock *rb = qemu_ram_block_by_name(block_name);
> +
> +    if (qemu_ram_pagesize(rb) > getpagesize()) {
> +        error_report("Postcopy doesn't support hugetlbfs yet (%s)", 
> block_name);

A small nitpick - I'd suggest  s/hugetlbfs/large page sizes/ as this error
will ultimately bubble up to users, and 'large page sizes' is the conceptual
feature


Regards,
Daniel
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