ceph: fix blindly expanding the readahead windows

Blindly expanding the readahead windows will cause unneccessary
pagecache thrashing and also will introduce the network workload.
We should disable expanding the windows if the readahead is disabled
and also shouldn't expand the windows too much.

Expanding forward firstly instead of expanding backward for possible
sequential reads.

Bound `rreq->len` to the actual file size to restore the previous page
cache usage.

The posix_fadvise may change the maximum size of a file readahead.

Cc: [email protected]
Fixes: 49870056005c ("ceph: convert ceph_readpages to ceph_readahead")
Link: https://lore.kernel.org/ceph-devel/[email protected]
Link: https://www.spinics.net/lists/ceph-users/msg76183.html
Signed-off-by: Xiubo Li <[email protected]>
Reviewed-and-tested-by: Hu Weiwen <[email protected]>
Reviewed-by: Milind Changire <[email protected]>
Signed-off-by: Ilya Dryomov <[email protected]>

0 files changed, 0 insertions, 0 deletions