On Wed, Oct 29, 2014 at 05:35:16PM +0100, Andrea Arcangeli wrote: > We can leverage the VM_FAULT_RETRY functionality in the page fault > paths better by using either get_user_pages_locked or > get_user_pages_unlocked. > > The former allow conversion of get_user_pages invocations that will > have to pass a "&locked" parameter to know if the mmap_sem was dropped > during the call. Example from: > > down_read(&mm->mmap_sem); > do_something() > get_user_pages(tsk, mm, ..., pages, NULL); > up_read(&mm->mmap_sem); > > to: > > int locked = 1; > down_read(&mm->mmap_sem); > do_something() > get_user_pages_locked(tsk, mm, ..., pages, &locked); > if (locked) > up_read(&mm->mmap_sem); > > The latter is suitable only as a drop in replacement of the form: > > down_read(&mm->mmap_sem); > get_user_pages(tsk, mm, ..., pages, NULL); > up_read(&mm->mmap_sem); > > into: > > get_user_pages_unlocked(tsk, mm, ..., pages); > > Where tsk, mm, the intermediate "..." paramters and "pages" can be any > value as before. Just the last parameter of get_user_pages (vmas) must > be NULL for get_user_pages_locked|unlocked to be usable (the latter > original form wouldn't have been safe anyway if vmas wasn't null, for > the former we just make it explicit by dropping the parameter). > > If vmas is not NULL these two methods cannot be used. > > Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> > Reviewed-by: Andres Lagar-Cavilla <andreslc@xxxxxxxxxx> > Reviewed-by: Peter Feiner <pfeiner@xxxxxxxxxx> 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>