On Fri, Aug 05, 2022 at 01:05:45AM -0700, Eric Biggers wrote: > On Wed, Aug 03, 2022 at 12:53:39PM +0200, Lukas Czerner wrote: > > diff --git a/include/linux/fs.h b/include/linux/fs.h > > index 9ad5e3520fae..2243797badf2 100644 > > --- a/include/linux/fs.h > > +++ b/include/linux/fs.h > > @@ -2245,9 +2245,9 @@ static inline void kiocb_clone(struct kiocb *kiocb, struct kiocb *kiocb_src, > > * The inode itself only has dirty timestamps, and the > > * lazytime mount option is enabled. We keep track of this > > * separately from I_DIRTY_SYNC in order to implement > > * lazytime. This gets cleared if I_DIRTY_INODE > > - * (I_DIRTY_SYNC and/or I_DIRTY_DATASYNC) gets set. I.e. > > - * either I_DIRTY_TIME *or* I_DIRTY_INODE can be set in > > - * i_state, but not both. I_DIRTY_PAGES may still be set. > > + * (I_DIRTY_SYNC and/or I_DIRTY_DATASYNC) gets set. But > > + * I_DIRTY_TIME can still be set if I_DIRTY_SYNC is already > > + * in place. > > I'm still having a hard time understanding the new semantics. The first > sentence above needs to be updated since I_DIRTY_TIME no longer means "the inode > itself only has dirty timestamps", right? The problem is that it was always assumed that I_DIRTY_INODE superseeds I_DIRTY_TIME and so it would get cleared in __mark_inode_dirty() when we have I_DIRTY_INODE. That's true, we call sb->s_op->dirty_inode(), the time update gets pushed into on-disk inode structure, I_DIRTY_TIME cleared and it will get queued for writeback. Any subsequent dirtying with I_DIRTY_TIME gets ignored simply because I_DIRTY_INODE is already set in i_state. But in ext4 this time update will never get pushed into on disk inode and there is no I_DIRTY_TIME so once the writeback is done we've lost all those I_DIRTY_TIME updates in between even if there was a sync. Now, we still clear I_DIRTY_TIME when we get I_DIRTY_INODE, but any subsequent I_DIRTY_TIME only updates won't be ignored and we set it into i_state. After the writeback is done it'll be moved to b_dirty_time list. So I am not sure how would you like it to be re-worded, simply removing the 'only' would be ok? > > Also, have you checked all the places that I_DIRTY_TIME is used and verified > they do the right thing now? What about inode_is_dirtytime_only()? Yes, that's fine, despite the slightly misleading name ;) > > Also what is the precise meaning of the flags argument to ->dirty_inode now? > > sb->s_op->dirty_inode(inode, > flags & (I_DIRTY_INODE | I_DIRTY_TIME)); > > Note that dirty_inode is documented in Documentation/filesystems/vfs.rst. Don't know. It alredy don't mention I_DIRTY_SYNC that can be there as well. Additionaly it can have I_DIRTY_TIME to inform the fs we have a dirty timestamp as well (in case of lazytime). Perhaps we can add: If the inode has dirty timestamp and lazytime is enabled I_DIRTY_TIME will be set in the flags. -Lukas > > - Eric >
