From: Pavel Begunkov > Sent: 09 December 2020 02:20 > > The block layer spends quite a while in blkdev_direct_IO() to copy and > initialise bio's bvec. However, if we've already got a bvec in the input > iterator it might be reused in some cases, i.e. when new > ITER_BVEC_FLAG_FIXED flag is set. Simple tests show considerable > performance boost, and it also reduces memory footprint. ... > @@ -398,7 +422,11 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_vecs) > bio->bi_end_io = blkdev_bio_end_io; > bio->bi_ioprio = iocb->ki_ioprio; > > - ret = bio_iov_iter_get_pages(bio, iter); > + if (iov_iter_is_bvec(iter) && iov_iter_bvec_fixed(iter)) > + ret = bio_iov_fixed_bvec_get_pages(bio, iter); > + else > + ret = bio_iov_iter_get_pages(bio, iter); > + Is it necessary to check iov_iter_is_bvec() as well as iov_iter_bvec_fixed() ? If so it is probably worth using & not && so the compiler stands a chance of generating a & (B | C) == B instead of 2 conditionals. (I think I saw the bits in the same field being tested. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
