Re: [PATCH -v2] ext4: enable scoped NOFS when starting a handle in nojournal mode

["Theodore Tso" <tytso@mit.edu>]

On Thu, Jul 16, 2026 at 01:45:51PM -0500, Andreas Dilger wrote:
> If you wanted to avoid an allocation for each nojournal handle on 64-bit
> systems, you could put a magic number in the high 32 bits of the handle
> pointer (which is unlikely to conflict with real memory addresses),
> and the PF_* flags in the low 32 bits.

That's an optimization we could do later, if we think the complexity
overhead is worth it.

> > @@ -513,6 +513,7 @@ struct jbd2_journal_handle
> >  	unsigned int h_sync: 1;
> >  	unsigned int h_reserved: 1;
> >  	unsigned int h_aborted: 1;
> > +	unsigned int h_invalid: 1;
> >  	unsigned int h_type: 8;
> >  	unsigned int h_line_no: 16;
> 
> Not sure if it makes much difference, but should h_line_no be aligned on a
> 16-bit offset and h_type aligned on an 8-bit offset by adding an
> "unsigned int h_unused:4" field before h_type, or reorder them so the 1-bit
> fields are at the end?  That would allow the integer fields to be accessed
> directly rather than also having to shift them.

Both gcc and clang support the extension of supporting bitfields on
char and shorts, so we can do this:

-       unsigned int    h_sync:         1;
-       unsigned int    h_reserved:     1;
-       unsigned int    h_aborted:      1;
-       unsigned int    h_invalid:      1;
-       unsigned int    h_type:         8;
-       unsigned int    h_line_no:      16;
+       unsigned char   h_sync:         1;
+       unsigned char   h_reserved:     1;
+       unsigned char   h_aborted:      1;
+       unsigned char   h_invalid:      1;
+       unsigned char   h_type;
+       unsigned short  h_line_no;

						- Ted