On Wed, Dec 22, 2010 at 05:37:57AM +0000, YAMAMOTO Takashi wrote: > hi, > > > Could you ack this discussion? > > sorry for dropping a ball. > > > > > On Tue, Dec 07, 2010 at 01:19:46AM +0900, Masao Uebayashi wrote: > >> On Thu, Nov 25, 2010 at 11:32:39PM +0000, YAMAMOTO Takashi wrote: > >> > [ adding cc: tech-kern@ ] > >> > > >> > hi, > >> > > >> > > On Wed, Nov 24, 2010 at 11:26:39PM -0800, Matt Thomas wrote: > >> > >> > >> > >> On Nov 24, 2010, at 10:47 PM, Masao Uebayashi wrote: > >> > >> > >> > >> > On Thu, Nov 25, 2010 at 05:44:21AM +0000, YAMAMOTO Takashi wrote: > >> > >> >> hi, > >> > >> >> > >> > >> >>> On Thu, Nov 25, 2010 at 04:18:25AM +0000, YAMAMOTO Takashi wrote: > >> > >> >>>> hi, > >> > >> >>>> > >> > >> >>>>> Hi, thanks for review. > >> > >> >>>>> > >> > >> >>>>> On Thu, Nov 25, 2010 at 01:58:04AM +0000, YAMAMOTO Takashi > >> > >> >>>>> wrote: > >> > >> >>>>>> hi, > >> > >> >>>>>> > >> > >> >>>>>> - what's VM_PHYSSEG_OP_PG? > >> > >> >>>>> > >> > >> >>>>> It's to lookup vm_physseg by "struct vm_page *", relying on that > >> > >> >>>>> "struct vm_page *[]" is allocated linearly. It'll be used to > >> > >> >>>>> remove > >> > >> >>>>> vm_page::phys_addr as we talked some time ago. > >> > >> >>>> > >> > >> >>>> i'm not sure if commiting this unused uncommented code now helps > >> > >> >>>> it. > >> > >> >>>> some try-and-benchmark cycles might be necessary given that > >> > >> >>>> vm_page <-> paddr conversion could be performace critical. > >> > >> >>> > >> > >> >>> If you really care performance, we can directly pass "struct > >> > >> >>> vm_page > >> > >> >>> *" to pmap_enter(). > >> > >> >>> > >> > >> >>> We're doing "struct vm_page *" -> "paddr_t" just before > >> > >> >>> pmap_enter(), > >> > >> >>> then doing "paddr_t" -> "vm_physseg" reverse lookup again in > >> > >> >>> pmap_enter() to check if a given PA is managed. What is really > >> > >> >>> needed here is, to lookup "struct vm_page *" -> "vm_physseg" once > >> > >> >>> and you'll know both paddr_t and managed or not. > >> > >> >> > >> > >> >> i agree that the current code is not ideal in that respect. > >> > >> >> otoh, i'm not sure if passing vm_physseg around is a good idea. > >> > >> > > >> > >> > It's great you share the interest. > >> > >> > > >> > >> > I chose vm_physseg, because it was there. I'm open to alternatives, > >> > >> > but I don't think you have many options... > >> > >> > >> > >> Passing vm_page * doesn't work if the page isn't managed since there > >> > >> won't be a vm_page for the paddr_t. > >> > >> > >> > >> Now passing both paddr_t and vm_page * would work and if the pointer > >> > >> to the vm_page, it would be an unmanaged mapping. This also gives the > >> > >> access to mdpg without another lookup. > >> > > > >> > > What if XIP'ed md(4), where physical pages are in .data (or .rodata)? > >> > > > >> > > And don't forget that you're the one who first pointed out that > >> > > allocating vm_pages for XIP is a pure waste of memory. ;) > >> > > >> > i guess matt meant "if the pointer to the vm_page is NULL,". > >> > > >> > > > >> > > I'm allocating vm_pages, only because of phys_addr and loan_count. > >> > > I believe vm_pages is unnecessary for read-only XIP segments. > >> > > Because they're read-only, and stateless. > >> > > > >> > > I've already concluded that the current "managed or not" model > >> > > doesn't work for XIP. I'm pretty sure that my vm_physseg + off_t > >> > > model can explain everything. I'm rather waiting for a counter > >> > > example how vm_physseg doesn't work... > >> > > >> > i guess your suggestion is too vague. > >> > where do you want to use vm_physseg * + off_t instead of vm_page * ? > >> > getpages, pmap_enter, and? how their function prototypes would be? > >> > >> The basic idea is straightforward; always allocate vm_physseg for > >> memories/devices. If a vm_physseg is used as general purpose > >> memory, you allocate vm_page[] (as vm_physseg::pgs). If it's > >> potentially mapped as cached, you allocate pvh (as vm_physseg:pvh). > > can you provide function prototypes?
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. 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. XIP pages don't need vm_page, but cached because it's vnode. (Just in case, have you read my paper?)