> the atime is updated, but not the mtime. Or do I need to set other flags on
> the inode to get the mtime updated ?
> My guess is that the first access cause VOP_GETPAGE to be called with
> VM_PROT_READ only, because the page is not mapped read/write. Then the write
> cause another page fault, but this one doesn't call VOP_GETPAGE().

unless the page was in hole, the first fault maps the page writable
and there is no second fault.

YAMAMOTO Takashi