On Tue, Apr 07, 2015 at 05:06:11PM +0300, Boaz Harrosh wrote: > > [v5] > Changed comments about pte_same check after the call to > pfn_mkwrite and the return value. > > [v4] > Kirill's comments about splitting out a new wp_pfn_shared(). > Add Documentation/filesystems/Locking text about pfn_mkwrite. > > [v3] > Kirill's comments about use of linear_page_index() > > [v2] > Based on linux-next/akpm [3dc4623]. For v4.1 merge window > Incorporated comments from Andrew And Kirill > > [v1] > This will allow FS that uses VM_PFNMAP | VM_MIXEDMAP (no page structs) > to get notified when access is a write to a read-only PFN. > > This can happen if we mmap() a file then first mmap-read from it > to page-in a read-only PFN, than we mmap-write to the same page. > > We need this functionality to fix a DAX bug, where in the scenario > above we fail to set ctime/mtime though we modified the file. > An xfstest is attached to this patchset that shows the failure > and the fix. (A DAX patch will follow) > > This functionality is extra important for us, because upon > dirtying of a pmem page we also want to RDMA the page to a > remote cluster node. > > We define a new pfn_mkwrite and do not reuse page_mkwrite because > 1 - The name ;-) > 2 - But mainly because it would take a very long and tedious > audit of all page_mkwrite functions of VM_MIXEDMAP/VM_PFNMAP > users. To make sure they do not now CRASH. For example current > DAX code (which this is for) would crash. > If we would want to reuse page_mkwrite, We will need to first > patch all users, so to not-crash-on-no-page. Then enable this > patch. But even if I did that I would not sleep so well at night. > Adding a new vector is the safest thing to do, and is not that > expensive. an extra pointer at a static function vector per driver. > Also the new vector is better for performance, because else we > Will call all current Kernel vectors, so to: > check-ha-no-page-do-nothing and return. > > No need to call it from do_shared_fault because do_wp_page is called to > change pte permissions anyway. > > CC: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > CC: Matthew Wilcox <matthew.r.wilcox@xxxxxxxxx> > CC: Jan Kara <jack@xxxxxxx> > CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > CC: Hugh Dickins <hughd@xxxxxxxxxx> > CC: Mel Gorman <mgorman@xxxxxxx> > CC: linux-mm@xxxxxxxxx > > Signed-off-by: Yigal Korman <yigal@xxxxxxxxxxxxx> > Signed-off-by: Boaz Harrosh <boaz@xxxxxxxxxxxxx> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> -- Kirill A. Shutemov -- 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>