On Mon, Sep 25, 2017 at 05:14:03PM -0600, Ross Zwisler wrote: > When mappings are created the vma->vm_flags that they use vary based on > whether the inode being mapped is using DAX or not. This setup happens in > XFS via mmap_region()=>call_mmap()=>xfs_file_mmap(). > > For us to be able to safely use the DAX per-inode flag we need to prevent > S_DAX transitions when any mappings are present, and we will do that by > looking at the address_space->i_mmap tree and returning -EBUSY if any > mappings are present. > > Unfortunately at the time that the filesystem's file_operations->mmap() > entry point is called the mapping has not yet been added to the > address_space->i_mmap tree. This means that at that point in time we > cannot determine whether or not the mapping will be set up to support DAX. > > Fix this by adding a new file_operations entry called post_mmap() which is > called after the mapping has been added to the address_space->i_mmap tree. > This post_mmap() op now happens at a time when we can be sure whether the > mapping will use DAX or not, and we can set up the vma->vm_flags > appropriately. Just like in the read/write path we'll need a flag that is passed down from the VM based on checking IS_DAX once and exactly once instead. -- 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>
