From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753087AbaKDL7J (ORCPT ); Tue, 4 Nov 2014 06:59:09 -0500 Received: from cantor2.suse.de ([195.135.220.15]:44340 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753036AbaKDL60 (ORCPT ); Tue, 4 Nov 2014 06:58:26 -0500 From: Jan Kara To: axboe@kernel.dk Cc: LKML , Jan Kara Subject: [PATCH] block: Expand a bit documentation about elevator_allow_merge_fn Date: Tue, 4 Nov 2014 12:52:41 +0100 Message-Id: <1415101961-18443-1-git-send-email-jack@suse.cz> X-Mailer: git-send-email 1.8.1.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Explain that two requests can be merged without elevator_allow_merge_fn() being called. Signed-off-by: Jan Kara --- Documentation/block/biodoc.txt | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) So in the end my discussion about request merging with the customer concluded similarly as ours wrt CFQ. It may be an issue but it happens rarely enough that it probably isn't worth an extra hook. I'm just sending a doc update because the fact that elevator_allow_merge_fn isn't called for all merges is somewhat surprising. diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt index 2101e718670d..82a0b0d8f4f3 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 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 -- 1.8.1.4