On Sun, Jan 10, 2016 at 5:59 AM, Boaz Harrosh <boaz@xxxxxxxxxxxxx> wrote: > Hi > > Today any VM_MIXEDMAP or VM_PFN mapping when enabling a write access > to their mapping, will have a double pagefault for every write access. > > This is because vma->vm_page_prot defines how a page/pfn is inserted into > the page table (see vma_wants_writenotify in mm/mmap.c). > > Which means that it is always inserted with read-only under the > assumption that we want to be notified when write access occurs. > > But this is not always true and adds an unnecessary page-fault on > every new mmap-write access > > This patchset is trying to give the fault handler more choice by passing > an pgprot_t to vm_insert_mixed() via a new vm_insert_mixed_prot() API. > > If the mm guys feel that the pgprot_t and its helpers and flags are private > to mm/memory.c I can easily do a new: vm_insert_mixed_rw() instead. of the > above vm_insert_mixed_prot() which enables any control not only write. > > Following is a patch to DAX to optimize out the extra page-fault. > > TODO: I only did 4k mapping perhaps 2M mapping can enjoy the same single > fault on write access. If interesting to anyone I can attempt a fix. > > Dan Andrew who needs to pick this up please? This collides with the patches currently pending in -mm for 4.5, lets take a look at this for 4.6. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>