On Wed, 30 Jan 2008, Andrea Arcangeli wrote: > On Wed, Jan 30, 2008 at 01:00:39AM +0100, Andrea Arcangeli wrote: > > get_user_pages, regular linux writes don't fault unless it's > > explicitly writeprotect, which is mandatory in a few archs, x86 not). > > actually get_user_pages doesn't fault either but it calls into > set_page_dirty, however get_user_pages (unlike a userland-write) at > least requires mmap_sem in read mode and the PT lock as serialization, > userland writes don't, they just go ahead and mark the pte in hardware > w/o faults. Anyway anonymous memory these days always mapped with > dirty bit set regardless, even for read-faults, after Nick finally > rightfully cleaned up the zero-page trick.
That is only partially true. pte are created wronly in order to track dirty state these days. The first write will lead to a fault that switches the pte to writable. When the page undergoes writeback the page again becomes write protected. Thus our need to effectively deal with page_mkclean. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
