On Wed, Jan 05, 2011 at 05:58:34AM +0000, YAMAMOTO Takashi wrote:
> hi,
>
> > I take silence as "no objection".
>
> the silence in this case means was-busy-for-other-things-and-forgot.
> sorry.
>
> >> I have no real code for this big picture at this moment. Making
> >> vm_physseg available as reference is the first step. This only
> >> changes uvm_page_physload() to return a pointer:
> >>
> >> -void uvm_page_physload();
> >> +void *uvm_page_physload();
> >>
> >> But this makes XIP pager MUCH cleaner. The reason has been explained
> >> many times.
>
> because the separate uvm_page_physload_device is no longer necessary,
> you mean? i have no problem with the step.
>
> >> Making fault handlers and pagers to use vm_physseg * + off_t is
> >> the next step, and I don't intend to work on it now. I just want
> >> to explain the big picture.
> >>
> >> >
> >> > >>
> >> > >> Keep vm_physseg * + off_t array on stack. If UVM objects uses
> >> > >> vm_page (e.g. vnode), its pager looks up vm_page -> vm_physseg *
> >> > >> + off_t *once* and cache it on stack.
> >> >
> >> > do you mean something like this?
> >> > struct {
> >> > vm_physseg *hoge;
> >> > off_t fuga;
> >> > } foo [16];
> >>
> >> Yes.
> >>
> >> Or cache vm_page * with it, like:
> >>
> >> struct vm_id {
> >> vm_physseg *seg;
> >> off_t off;
> >> vm_page *pg;
> >> };
> >>
> >> uvm_fault()
> >> {
> >> vm_id pgs[];
> >> :
> >> }
> >>
> >> Vnode pager (genfs_getpages) takes vm_page's by looking up
> >> vnode::v_uobj's list, or uvn_findpages().
> >>
> >> When it returns back to fault handler, we have to lookup vm_physseg
> >> for each page. Then fill the "seg" slot above (assuming we'll
> >> remove vm_page::phys_addr soon).
> >>
> >> Fault handler calls per-vm_page operations iff vm_page slot is filled.
> >> XIP pages are not pageq'ed.
>
> pgo_get returns either seg+off or pg for each vm_id slots?
vm_id[] is passed to pgo_get, each pgo_get (uvn_get, udv_get, ...)
will fill seg + off and return the array back to uvm_fault.
Pagers that use vm_page (e.g. vnode) will get pg from vnode, then
lookup seg+off, fill them into the vm_id slot.
Those that don't use vm_page (e.g. cdev) will get seg+off from
underlying objects, fill them into the vm_id slot, and return.
>
> >> XIP pages don't need vm_page, but
> >> cached because it's vnode.
>
> can you explain this sentence?
Sorry, it was so unclear.
XIP pages don't need vm_page (as a paging state variable),
because the pages are read-only and never involve paging.
XIP pages have to be mapped as cacheable at MMU level,
because it's vnode.
I'm allocating the full vm_page for XIP'able pages, only because
chs@ wanted to support loaning, which needs vm_page::loan_count.
>
> >> (Just in case, have you read my paper?)
>
> which paper? i guess no.
http://uebayasi.dyndns.org/~uebayasi/tmp/xip.pdf
>
> YAMAMOTO Takashi
--
Masao Uebayashi / Tombi Inc. / Tel: +81-90-9141-4635
