On Wed, Nov 10, 2010 at 06:47:28AM +0800, Andrew Morton wrote: > On Tue, 09 Nov 2010 07:09:21 +0800 > Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote: > > > In WB_SYNC_ALL mode, filesystems are not expected to skip dirty pages on > > temporal lock contentions or non fatal errors, otherwise sync() will > > return without actually syncing the skipped pages. Add a check to > > catch possible redirty_page_for_writepage() callers that violate this > > expectation. > > > > I'd recommend to keep this check in -mm tree for some time and fixup the > > possible warnings before pushing it to upstream. > > > > Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > > --- > > fs/fs-writeback.c | 1 + > > 1 file changed, 1 insertion(+) > > > > --- linux-next.orig/fs/fs-writeback.c 2010-11-07 22:01:06.000000000 +0800 > > +++ linux-next/fs/fs-writeback.c 2010-11-07 22:01:15.000000000 +0800 > > @@ -527,6 +527,7 @@ static int writeback_sb_inodes(struct su > > * buffers. Skip this inode for now. > > */ > > redirty_tail(inode); > > + WARN_ON_ONCE(wbc->sync_mode == WB_SYNC_ALL); > > } > > spin_unlock(&inode_lock); > > iput(inode); > > This is quite kernel-developer-unfriendly. > > Suppose the warning triggers. Now some poor schmuck looks at the > warning and doesn't have a *clue* why it was added. He has to run off > and grovel through git trees finding changelogs, which is a real pain > if the code has been trivially altered since it was first added. > > As a general rule, a kernel developer should be able to look at a > warning callsite and then work out why the warning was emitted! > > > IOW, you owe us a code comment, please. Good point! I'll add this comment. + /* + * There's no logic to retry skipped pages for sync(), + * filesystems are assumed not to skip dirty pages on + * temporal lock contentions or non fatal errors. + */ + WARN_ON_ONCE(wbc->sync_mode == WB_SYNC_ALL); IOW, if some FS triggers this warning and it's non-trivial to fix the FS, we'll have to work out a sync retry scheme for skipped pages. Thanks, Fengguang -- 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>