Yes. The basic unit of IO in there is a 64k BIO. So once readahead
is cruising, pages come unlocked in 16-page batches. In 2.4 they'll
come unlocked one at a time against a device such as a floppy drive.
But with default settings the readahead code lays one to two of these
BIOs out ahead of the read point, so the application never stumbles across
a locked page unless it's outpacing the device.
At least that's the theory, and the testing I did yesterday
So I'd appreciate it if Simon could invetigate a little further
with the test app I posted. Something is up, and it may not
be just an NFS thing. But note that nfs_readpage will go
synchronous if rsize is less than PAGE_CACHE_SIZE, so it has
to be set up right.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to email@example.com
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/