On Wed, Nov 17, 2010 at 04:53:09PM -0800, Andrew Morton wrote: > On Wed, 17 Nov 2010 18:52:30 -0500 > "Ted Ts'o" <tytso@xxxxxxx> wrote: > > > On Thu, Nov 18, 2010 at 10:11:43AM +1100, Dave Chinner wrote: > > > I don't think ->page_mkwrite can be worked around - we need that to > > > be called on the first write fault of any mmap()d page to ensure it > > > is set up correctly for writeback. If we don't get write faults > > > after the page is mlock()d, then we need the ->page_mkwrite() call > > > during the mlock() call. > > > > OK, so I'm not an mm hacker, so maybe I'm missing something. Could > > part of this be fixed by simply sending the write faults for > > mlock()'ed pages, so page_mkwrite() gets called when the page is > > dirtied. Seems like a real waste to have the file system pre-allocate > > all of the blocks for a mlock()'ed region. Why does mlock() have to > > result in the write faults getting suppressed when the page is > > actually dirtied? This is actually what the patch does - by having mlock() use a read fault, pages are loaded in memory and mlocked, but the ptes are not marked as writable so that a later write access will be caught as a write fault at that time (with all the usual dirtying and page_mkwrite() callbacks). > Yup, I don't think it would be too bad to take a minor fault each time > an mlocked page transitions from clean->dirty. > > In fact we should already be doing that, after the mlocked page gets > written back by kupdate? Hope so! Yes, handle_mm_fault() is careful to never create writable ptes pointing to clean file pages, so that a later write fault will correctly dirty the corresponding page. -- Michel "Walken" Lespinasse A program is never fully debugged until the last user dies. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>