On Thu, May 28, 2009 at 10:27:11AM +0200, Jan Kara wrote: > On Wed 27-05-09 21:28:07, Aneesh Kumar K.V wrote: > > Even with changes to make pages writeprotech on truncate/i_size update we > > can still see buffer_heads which are not mapped in the writepage > > callback. Consider the below case. > > > > 1) truncate(f, 1024) > > 2) mmap(f, 0, 4096) > > 3) a[0] = 'a' > > 4) truncate(f, 4096) > > 5) writepage(...) > > > > Now if we get a writepage callback immediately after (4) and before an > > attempt to write at any other offset via mmap address (which implies we > > are yet to get a pagefault and do a get_block) what we would have is the > > page which is dirty have first block allocated and the other three > > buffer_heads unmapped. > > > > In the above case the writepage should go ahead and try to write > > the first blocks and clear the page_dirty flag. Because the further > > attempt to write to the page will again create a fault and result in > > allocating blocks and marking page dirty. Also if we don't write > > any other offset via mmap address we would still have written the first > > block to the disk and rest of the space will be considered as a hole. > OK, but this requires my patches to not cause data loss, doesn't it? > Nothing prevents user from writing data into the full page just after > truncate(f, 4096) before the writepage is called. And without my patches, > fault will not happen for such user write. > Just that we should have this dependency in mind. Otherwise the patch > looks fine to me. Yes the entire series is on top of your patches -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
