From: Kiyoshi Ueda Date: Fri, 17 Jun 2005 14:15:10 +0000 (+0200) Subject: When cfq I/O scheduler is selected, get_request() in __make_request() calls X-Git-Tag: v2.6.12~1^2 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=db3b5848ea6440968fcdd29b80514d0de044bb7c;p=pandora-kernel.git When cfq I/O scheduler is selected, get_request() in __make_request() calls __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: Jens Axboe Signed-off-by: Kiyoshi Ueda Signed-off-by: Jun'ichi Nomura --- Reading git-diff-tree failed