linux-kernel - Re: [PATCH 05/10] block: remove per-queue plugging

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Date:	Mon, 18 Apr 2011 14:19:01 +1000
From:	NeilBrown <neilb@...e.de>
To:	Jens Axboe <jaxboe@...ionio.com>
Cc:	Mike Snitzer <snitzer@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hch@...radead.org" <hch@...radead.org>,
	"dm-devel@...hat.com" <dm-devel@...hat.com>,
	"linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>
Subject: Re: [PATCH 05/10] block: remove per-queue plugging

On Mon, 18 Apr 2011 08:19:22 +1000 NeilBrown <neilb@...e.de> wrote:

> So can we please have my original patch applied? (Revised version using
> list_splice_init included below).

I hadn't adjusted that one properly for the recent code shuffling.
This one is actually tested...

Thanks,
NeilBrown

>From 325b1c12b6165002022bd7b599f95c0331491cb3 Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@...e.de>
Date: Mon, 18 Apr 2011 14:06:05 +1000
Subject: [PATCH] Enhance new plugging support to support general callbacks.

md/raid requires an unplug callback, but as it does not uses
requests the current code cannot provide one.

So allow arbitrary callbacks to be attached to the blk_plug.

Cc: Jens Axboe <jaxboe@...ionio.com>
Signed-off-by: NeilBrown <neilb@...e.de>
---
 block/blk-core.c       |   20 ++++++++++++++++++++
 include/linux/blkdev.h |    7 ++++++-
 2 files changed, 26 insertions(+), 1 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 78b7b0c..77edf05 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2638,6 +2638,7 @@ void blk_start_plug(struct blk_plug *plug)
 
 	plug->magic = PLUG_MAGIC;
 	INIT_LIST_HEAD(&plug->list);
+	INIT_LIST_HEAD(&plug->cb_list);
 	plug->should_sort = 0;
 
 	/*
@@ -2678,6 +2679,24 @@ static void queue_unplugged(struct request_queue *q, unsigned int depth,
 		q->unplugged_fn(q);
 }
 
+static void flush_plug_callbacks(struct blk_plug *plug)
+{
+	LIST_HEAD(callbacks);
+
+	if (list_empty(&plug->cb_list))
+		return;
+
+	list_splice_init(&plug->cb_list, &callbacks);
+
+	while (!list_empty(&callbacks)) {
+		struct blk_plug_cb *cb = list_first_entry(&callbacks,
+							  struct blk_plug_cb,
+							  list);
+		list_del(&cb->list);
+		cb->callback(cb);
+	}
+}
+
 void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 {
 	struct request_queue *q;
@@ -2688,6 +2707,7 @@ void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 
 	BUG_ON(plug->magic != PLUG_MAGIC);
 
+	flush_plug_callbacks(plug);
 	if (list_empty(&plug->list))
 		return;
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index ec0357d..f3f7879 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -860,8 +860,13 @@ extern void blk_put_queue(struct request_queue *);
 struct blk_plug {
 	unsigned long magic;
 	struct list_head list;
+	struct list_head cb_list;
 	unsigned int should_sort;
 };
+struct blk_plug_cb {
+	struct list_head list;
+	void (*callback)(struct blk_plug_cb *);
+};
 
 extern void blk_start_plug(struct blk_plug *);
 extern void blk_finish_plug(struct blk_plug *);
@@ -887,7 +892,7 @@ static inline bool blk_needs_flush_plug(struct task_struct *tsk)
 {
 	struct blk_plug *plug = tsk->plug;
 
-	return plug && !list_empty(&plug->list);
+	return plug && (!list_empty(&plug->list) || !list_empty(&plug->cb_list));
 }
 
 /*
-- 
1.7.3.4

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