Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize()

[David Hildenbrand]

On 24.02.20 11:50, David Hildenbrand wrote:
> On 19.02.20 23:46, Peter Xu wrote:
>> On Wed, Feb 12, 2020 at 02:42:46PM +0100, David Hildenbrand wrote:
>>> Factor it out and add a comment.
>>>
>>> Reviewed-by: Igor Kotrasinski <address@hidden>
>>> Acked-by: Murilo Opsfelder Araujo <address@hidden>
>>> Reviewed-by: Richard Henderson <address@hidden>
>>> Cc: "Michael S. Tsirkin" <address@hidden>
>>> Cc: Murilo Opsfelder Araujo <address@hidden>
>>> Cc: Greg Kurz <address@hidden>
>>> Cc: Eduardo Habkost <address@hidden>
>>> Cc: "Dr. David Alan Gilbert" <address@hidden>
>>> Cc: Igor Mammedov <address@hidden>
>>> Signed-off-by: David Hildenbrand <address@hidden>
>>> ---
>>>  util/mmap-alloc.c | 21 ++++++++++++---------
>>>  1 file changed, 12 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
>>> index 27dcccd8ec..82f02a2cec 100644
>>> --- a/util/mmap-alloc.c
>>> +++ b/util/mmap-alloc.c
>>> @@ -82,17 +82,27 @@ size_t qemu_mempath_getpagesize(const char *mem_path)
>>>      return qemu_real_host_page_size;
>>>  }
>>>  
>>> +static inline size_t mmap_pagesize(int fd)
>>> +{
>>> +#if defined(__powerpc64__) && defined(__linux__)
>>> +    /* Mappings in the same segment must share the same page size */
>>> +    return qemu_fd_getpagesize(fd);
>>> +#else
>>> +    return qemu_real_host_page_size;
>>> +#endif
>>> +}
>>
>> Pure question: This will return 4K even for huge pages on x86, is this
>> what we want?
> 
> (was asking myself the same question) I *think* it's intended. It's
> mainly only used to allocate one additional guard page. The callers of
> qemu_ram_mmap() make sure that the size is properly aligned (e.g., to
> huge pages).
> 
> Of course, a 4k guard page is sufficient - unless we can't use that
> (special case for ppc64 here).
> 
> Thanks!
> 

We could rename the function to mmap_guard_pagesize(), thoughts?

-- 
Thanks,

David / dhildenb