• Kiyoshi Ueda 's avatar
    When cfq I/O scheduler is selected, get_request() in __make_request() calls · db3b5848
    Kiyoshi Ueda authored
    
    __cfq_get_queue().  __cfq_get_queue() finds an existing queue (struct
    cfq_queue) of the current process for the device and returns it.  If it's not
    found, __cfq_get_queue() creates and returns a new one if __cfq_get_queue() is
    called with __GFP_WAIT flag, or __cfq_get_queue() returns NULL (this means that
    get_request() fails) if no __GFP_WAIT flag.
    
    On the other hand, in __make_request(), get_request() is called without
    __GFP_WAIT flag at the first time.  Thus, the get_request() fails when there is
    no existing queue, typically when it's called for the first I/O request of the
    process to the device.
    
    Though it will be followed by get_request_wait() for general case,
    __make_request() will just end the I/O with an error (EWOULDBLOCK) when the
    request was for read-ahead.
    Signed-off-by: default avatarJens Axboe <axboe@suse.de>
    Signed-off-by: default avatarKiyoshi Ueda <k-ueda@ct.jp.nec.com>
    Signed-off-by: default avatarJun'ichi Nomura <j-nomura@ce.jp.nec.com>
    db3b5848
cfq-iosched.c 43.3 KB