Hi All, Sorry for making some confusions. I missed the nopage call back in the vm_operations struct. This call back function is responsible for locating the pages in page cache and getting data from disk. In case of backed files, filemap_nopage in mm/filemap.c does this. Regards, Shameem ----- Original Message ---- > From: Shameem Ahamed <shameem.ahamed@xxxxxxxxx> > To: shailesh jain <coolworldofshail@xxxxxxxxx>; Ed Cashin <ecashin@xxxxxxxxxx> > Cc: kernelnewbies@xxxxxxxxxxxx > Sent: Tue, November 10, 2009 6:00:20 PM > Subject: Re: Difference between major page fault and minor page fault > > Hi Ed, Shailesh, > > Thanks for the replies. > > I have gone through the handle_pte_fault function in memory.c > > It seems like, it handles VM page faults. I am more concerned with the physical > page faults. As i can see from the code, it allocates new pages for the VMA. > But if the VMA is backed by a disk file the contents of the file should also be > read to the RAM. VM_FAULT_MINOR and VM_FAULT_MAJOR are related to VM minor > faults and major faults. > > I want to get more information regarding the physical page faults. Once the > process is created VMA for the process created, and VM pages are allocated on > demand (when the fault occurs) and the data will be read from DISK to RAM if it > is not present. > > Eg: I am running an application, called EG. When EG is started VMA for EG will > be created, virtual pages will be allocated and a txt, data, and other required > parts of EG will be loaded and mapped to the virtual pages. > > > I am looking out for the function which copies pages from disk to ram. > > Can anyone please help me ?. > > Regards, > Shameem > > ----- Original Message ---- > > From: shailesh jain > > To: Ed Cashin > > Cc: kernelnewbies@xxxxxxxxxxxx > > Sent: Tue, November 10, 2009 3:23:59 AM > > Subject: Re: Difference between major page fault and minor page fault > > > > Minor faults can occur at many places: > > > > 1) Shared pages among processes/ Swap cache - A process can take a > > page fault when the page is already present in the swap cache. This > > will be minor fault since you will not go to disk. > > > > 2) COW but no fork - Memory is not allocated initially for malloc. It > > will point to global zero page, however when the process attempts to > > write to it you will get minor page fault. > > > > 3) Stack is expanding. Check if the fault occurred closed to the > > bottom the stack, if yes then let's allocate page under the assumption > > that stack is expanding. > > > > 4) Vmalloc address space. Page fault can occur in kernel address space > > for vmalloc area. When this happens you sync up process' page tables > > with master page table (init_mm). > > > > 5) COW for fork. > > > > > > Shailesh Jain > > > > On Mon, Nov 9, 2009 at 7:08 AM, Ed Cashin wrote: > > > Shameem Ahamed writes: > > > > > >> Hi, > > >> > > >> Can anyone explain the difference between major and minor page faults. > > >> > > >> As far as I know, major page fault follows a disk access to retrieve > > >> the data. Minor page fault occurs mainly for COW pages. Is there any > > >> other instances other than COW, where there will be a minor page > > >> fault. Which kernel function handles the major page fault ?. > > > > > > Ignoring error cases, arch/x86/mm/fault.c:do_page_fault calls > > > mm/memory.c:handle_mm_fault and looks for the flags, VM_FAULT_MAJOR or > > > VM_FAULT_MINOR in the returned value, so the definitive answer is in > > > how that return value gets set. The handle_mm_fault value comes from > > > called function hugetlb_fault or handle_pte_fault (again, ignoring > > > error conditions). I'd suggest starting your inquiry by looking at > > > the logic in handle_pte_fault. > > > > > >> Also, can anyone please confirm that in 2.6 kernels, page cache and > > >> buffer cache are normalized ?. Now we have only one cache, which > > >> includes both buffer cache and page cache. > > > > > > They were last I heard. Things move so fast these days that I can't > > > keep up! :) > > > > > > -- > > > Ed Cashin > > > Find experimental aoe Linux driver patches at > > > http://coraid.typepad.com/aoe_linux_proving_grounds/ > > > > > > > > > -- > > > To unsubscribe from this list: send an email with > > > "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx > > > Please read the FAQ at http://kernelnewbies.org/FAQ > > > > > > > > > > -- > > To unsubscribe from this list: send an email with > > "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx > > Please read the FAQ at http://kernelnewbies.org/FAQ > > > > > > -- > To unsubscribe from this list: send an email with > "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx > Please read the FAQ at http://kernelnewbies.org/FAQ -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
