Re: Device page

[yamt%mwd.biglobe.ne.jp@localhost (YAMAMOTO Takashi)]

> On Feb 2, 2010, at 10:20 AM, Masao Uebayashi wrote:
> 
>> As I briefly mentioned before, I'll need device page to support XIP.  It's
>> a struct vm_page *, which is actually a magic value which conveys data from
>> pgo_get() to pmap_enter().
>> 
>> When a device page is pmap_enter()'ed, pmap checks if it's a device page or
>> not, if so, stores a PV into a dedicated vm_physseg for devices.  When a
>> device page is passed to pmap_page_*() (struct vm_page *-oriented functions),
>> they look for the device vm_physseg, look up a PV header, then look up a PV.
>> 
>> I also want to make these minimal PV handling moved to some MI place - 
>> probably
>> uvm_page.c.  Now we don't define MI PV header yet, I'll allocate struct
>> vm_page_md *[] for each XIP-capable device.  This will be put in uvm_page.c
>> too.
> 
> I'd rather change the arguments to pmap_{zero,copy}_page from paddr_t to 
> struct vm_page * since it's easier to fetch the physical address from the 
> page than getting the vm_page from the pa.

recording physical adderess in each vm_page wastes space given that vm_page
is allocated as an array.
ie. if we have a way to find the corresponding physseg from a vm_page,
its corresponding physical address can be calculated.
so i hesitate to propagate the assumption of fast VM_PAGE_TO_PHYS.

YAMAMOTO Takashi

> 
> It also means that you can easily have a VM_PAGE_DEVICE_PAGE_P(pg) macro to 
> detect whether this page is a device page or not.  No need for the pmap to 
> know what physseg it is in.