From: Jan Kara Date: Tue, 4 Nov 2014 11:52:41 +0000 (+0100) Subject: block: Expand a bit documentation about elevator_allow_merge_fn X-Git-Tag: v3.19-rc1~88^2~22 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=b8ab956c544e51a8d19ea3f38b54355d6aa92c33;p=karo-tx-linux.git block: Expand a bit documentation about elevator_allow_merge_fn Explain that two requests can be merged without elevator_allow_merge_fn() being called. Signed-off-by: Jan Kara Signed-off-by: Jens Axboe --- diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt index 2101e718670d..f1323c6b7ed2 100644 --- a/Documentation/block/biodoc.txt +++ b/Documentation/block/biodoc.txt @@ -946,7 +946,11 @@ elevator_allow_merge_fn called whenever the block layer determines request safely. The io scheduler may still want to stop a merge at this point if it results in some sort of conflict internally, - this hook allows it to do that. + this hook allows it to do that. Note however + that two *requests* can still be merged at later + time. Currently the io scheduler has no way to + prevent that. It can only learn about the fact + from elevator_merge_req_fn callback. elevator_dispatch_fn* fills the dispatch queue with ready requests. I/O schedulers are free to postpone requests by