[Xen-devel] [PATCH v2 02/20] xen: Introduce a function to split a Linux page into Xen page
julien.grall at citrix.com
Fri Jul 24 03:20:57 PDT 2015
On 24/07/15 11:10, David Vrabel wrote:
> On 24/07/15 10:54, Julien Grall wrote:
>> On 24/07/15 10:31, David Vrabel wrote:
>>> On 09/07/15 21:42, Julien Grall wrote:
>>>> The Xen interface is always using 4KB page. This means that a Linux page
>>>> may be split across multiple Xen page when the page granularity is not
>>>> the same.
>>>> This helper will break down a Linux page into 4KB chunk and call the
>>>> helper on each of them.
>>>> --- a/include/xen/page.h
>>>> +++ b/include/xen/page.h
>>>> @@ -39,4 +39,24 @@ struct xen_memory_region xen_extra_mem[XEN_EXTRA_MEM_MAX_REGIONS];
>>>> extern unsigned long xen_released_pages;
>>>> +typedef int (*xen_pfn_fn_t)(struct page *page, unsigned long pfn, void *data);
>>>> +/* Break down the page in 4KB granularity and call fn foreach xen pfn */
>>>> +static inline int xen_apply_to_page(struct page *page, xen_pfn_fn_t fn,
>>>> + void *data)
>>> I think this should be outlined (unless you have measurements that
>>> support making it inlined).
>> I don't have any performance measurements. Although, when Linux is using
>> 4KB page granularity, the loop in this helper will be dropped by the
>> helper. The code would look like:
>> unsigned long pfn = xen_page_to_pfn(page);
>> ret = fn(page, fn, data);
>> if (ret)
>> return ret;
>> The compiler could even inline the callback (fn). So it drops 2
>> functions call.
> Ok, keep it inlined.
>>> Also perhaps make it
>>> int xen_for_each_gfn(struct page *page,
>>> xen_gfn_fn_t fn, void *data);
>> gfn standing for Guest Frame Number right?
> Yes. This suggestion is just changing the name to make it more obvious
> what it does.
I will change the name.
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