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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 <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Jan Kara 2014-11-04 12:52:41 +01:00 committed by Jens Axboe
parent e167dfb53c
commit b8ab956c54
1 changed files with 5 additions and 1 deletions
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6
Documentation/block/biodoc.txt
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@ -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