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authorJan Kara <jack@suse.cz>2014-11-04 12:52:41 +0100
committerJens Axboe <axboe@fb.com>2014-11-04 16:28:15 +0100
commitb8ab956c544e51a8d19ea3f38b54355d6aa92c33 (patch)
tree98cb2d607852e0f69c6b9cddaec479429460c732 /Documentation/block
parentblk-mq: add BLK_MQ_F_DEFER_ISSUE support flag (diff)
downloadlinux-b8ab956c544e51a8d19ea3f38b54355d6aa92c33.tar.xz
linux-b8ab956c544e51a8d19ea3f38b54355d6aa92c33.zip
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>
Diffstat (limited to 'Documentation/block')
-rw-r--r--Documentation/block/biodoc.txt6
1 files changed, 5 insertions, 1 deletions
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