bio: skip atomic inc/dec of ->bi_cnt for most use cases
Struct bio has a reference count that controls when it can be freed.
Most uses cases is allocating the bio, which then returns with a
single reference to it, doing IO, and then dropping that single
reference. We can remove this atomic_dec_and_test() in the completion
path, if nobody else is holding a reference to the bio.
If someone does call bio_get() on the bio, then we flag the bio as
now having valid count and that we must properly honor the reference
count when it's being put.
Tested-by: Robert Elliott <elliott@hp.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 8bfe9ee..7486ea1 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -290,7 +290,21 @@
* returns. and then bio would be freed memory when if (bio->bi_flags ...)
* runs
*/
-#define bio_get(bio) atomic_inc(&(bio)->bi_cnt)
+static inline void bio_get(struct bio *bio)
+{
+ bio->bi_flags |= (1 << BIO_REFFED);
+ smp_mb__before_atomic();
+ atomic_inc(&bio->__bi_cnt);
+}
+
+static inline void bio_cnt_set(struct bio *bio, unsigned int count)
+{
+ if (count != 1) {
+ bio->bi_flags |= (1 << BIO_REFFED);
+ smp_mb__before_atomic();
+ }
+ atomic_set(&bio->__bi_cnt, count);
+}
enum bip_flags {
BIP_BLOCK_INTEGRITY = 1 << 0, /* block layer owns integrity data */