ceph: fix blindly expanding the readahead windows
commit dc94bb8f upstream. 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: stable@vger.kernel.org Fixes: 49870056 ("ceph: convert ceph_readpages to ceph_readahead") Link: https://lore.kernel.org/ceph-devel/20230504082510.247-1-sehuww@mail.scut.edu.cn Link: https://www.spinics.net/lists/ceph-users/msg76183.html Signed-off-by: Xiubo Li <xiubli@redhat.com> Reviewed-and-tested-by: Hu Weiwen <sehuww@mail.scut.edu.cn> Reviewed-by: Milind Changire <mchangir@redhat.com> Signed-off-by: Ilya Dryomov <idryomov@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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