On Tue, Mar 24, 2015 at 09:26:58AM -0600, Jens Axboe wrote: > The top bits of bio->bi_flags are reserved for keeping the > allocation pool, set aside the next four bits for carrying > a stream ID. That leaves us with support for 15 streams, > 0 is reserved as a "stream not set" value. > > Add helpers for setting/getting stream ID of a bio. .... > +/* > + * after the pool bits, next 4 bits are for the stream id > + */ > +#define BIO_STREAM_BITS (4) > +#define BIO_STREAM_OFFSET (BITS_PER_LONG - 8) > +#define BIO_STREAM_MASK ((1 << BIO_STREAM_BITS) - 1) > + > +static inline unsigned long streamid_to_flags(unsigned int id) > +{ > + return (unsigned long) (id & BIO_STREAM_MASK) << BIO_STREAM_OFFSET; > +} > + > +static inline void bio_set_streamid(struct bio *bio, unsigned int id) > +{ > + bio->bi_flags |= streamid_to_flags(id); > +} > + > +static inline unsigned int bio_get_streamid(struct bio *bio) > +{ > + return (bio->bi_flags >> BIO_STREAM_OFFSET) & BIO_STREAM_MASK; > +} > + > +static inline bool bio_streamid_valid(struct bio *bio) > +{ > + return bio_get_streamid(bio) != 0; > +} Need to reserve at least one stream for filesystem private use (e.g. metadata writeback). Potentially 2 streams - one for the journal which is frequently overwritten, the other for all other long lived persistent metadata. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html