On Thu, May 28, 2009 at 09:03:41AM -0400, Josef Bacik wrote: > On Wed, May 27, 2009 at 03:01:00PM +0200, Jan Kara wrote: > > > > Sorry, another possibly braindead question. When we extend the i_size you make > it so that the page will be faulted the next time it's written to via > page_mkclean, which from what I can tell is done via pte_wrprotect. The problem > with this is the next time we write to the page, we do pte_mkwrite, which makes > it so that we won't fault the next time we write, correct? So if I were to do > > ftruncate(fd, 0); > pwrite(fd, buf, 1024, 0); > map = mmap(NULL, 4096, PROT_WRITE, MAP_SHARED, fd, 0); > map[0] = 'a'; > ftruncate(fd, 10000); > map[0] = 'b'; --> causes a page fault again This will do block allocation for the entire page within i_size. (ie multiple blocks) ext4_page_mkwrite have size = i_size_read(..) if (page->index == size >> PAGE_CACHE_SHIFT) len = size & ~PAGE_CACHE_MASK; else len = PAGE_CACHE_SIZE; > memset(map, 'a', 4096); --> wouldn't cause a pagefault > writepage at some point > > We'd still be in the position that you are trying to solve, correct, since we > will have dirtied the rest of the page without calling mkwrite for the other > sections of it, which would result in unallocated blocks when we hit writepage. > Thanks, > -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
