Re: [PATCH 3/4] Swapping

[Anthony Liguori <anthony-rdkfGonbjUSkNkDKm+mE6A@public.gmane.org>]

Avi Kivity wrote:
> Anthony Liguori wrote:
>> Avi Kivity wrote:
>>> Anthony Liguori wrote:
>>>  
>>>> I think it's just a matter of calling do_mmap() with the 
>>>> appropriate parameters.  It looks likes there's some drivers call 
>>>> do_mmap() directly.
>>>>
>>>>       
>>>
>>> This will halve the maximum size of virtual machines on i386 since
>>> userspace will also mmap() the memory, and the virtual address space is
>>> restricted to 3GB.
>>>   
>>
>> I wonder if there is a way to force the mmap() to return the 
>> userspace address we previously allocated.
>>
>
> Yes:
>
>>
>> unsigned long
>> get_unmapped_area(struct file *file, unsigned long addr, unsigned 
>> long len,
>>                 unsigned long pgoff, unsigned long flags)
>> {
>>         unsigned long (*get_area)(struct file *, unsigned long,
>>                                   unsigned long, unsigned long, 
>> unsigned long);
>>
>>         get_area = current->mm->get_unmapped_area;
>>         if (file && file->f_op && file->f_op->get_unmapped_area)
>>                 get_area = file->f_op->get_unmapped_area;
>>         addr = get_area(file, addr, len, pgoff, flags);

Hrm, so you can return the area that should be used but you still 
install vma_ops?  Wouldn't that result in an infinite loop when 
userspace attempted to map the area since we'll try to satisfy the 
nopage handler by doing a get_user_pages?

Regards,

Anthony Liguori



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