On 01/11/2016 03:19 AM, Dan Williams wrote: > 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. > OK thanks, I will try to work this over current linux-next and sure we will wait for 4.5-rc1 to look at this again. Do you have any comments in general about this? Thanks Boaz -- 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>