linux-kernel - [PATCH v2] writeback: mark sysctl vm.block

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Date:	Tue, 15 Jan 2013 08:28:13 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	linux-kernel@...r.kernel.org, chavey@...gle.com,
	fengguang.wu@...el.com, Jan Kara <jack@...e.cz>
Subject: [PATCH v2] writeback: mark sysctl vm.block_dump for removal

vm.block_dump is nasty in that it dumps IO traces directly to printk.
It isn't scalable and can easily lead to looping behavior - IO
generating kernel message which in turn genreates log IO, ad
infinitum.

Now that proper tracepoints are in place, vm.block_dump isn't
necessary.  Generate a warning if used so that it can be removed down
the road.

Cc: Added contact info as suggested by Jan.

Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: Jan Kara <jack@...e.cz>
---
 include/linux/writeback.h |    3 +++
 kernel/sysctl.c           |    2 +-
 mm/page-writeback.c       |   15 +++++++++++++++
 patches/series            |    1 +
 4 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index b82a83a..678ee6d 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -143,6 +143,9 @@ extern int dirty_ratio_handler(struct ctl_table *table, int write,
 extern int dirty_bytes_handler(struct ctl_table *table, int write,
 		void __user *buffer, size_t *lenp,
 		loff_t *ppos);
+extern int block_dump_handler(struct ctl_table *table, int write,
+		void __user *buffer, size_t *lenp,
+		loff_t *ppos);
 
 struct ctl_table;
 int dirty_writeback_centisecs_handler(struct ctl_table *, int,
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index c88878d..9e7f7b5 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1288,7 +1288,7 @@ static struct ctl_table vm_table[] = {
 		.data		= &block_dump,
 		.maxlen		= sizeof(block_dump),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec,
+		.proc_handler	= block_dump_handler,
 		.extra1		= &zero,
 	},
 	{
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 6f42712..605632d 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -390,6 +390,21 @@ int dirty_bytes_handler(struct ctl_table *table, int write,
 	return ret;
 }
 
+int block_dump_handler(struct ctl_table *table, int write,
+		       void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	static bool warned = false;
+	int ret;
+
+	ret = proc_dointvec(table, write, buffer, lenp, ppos);
+	if (!warned && block_dump) {
+		pr_warning("sysctl: vm.block_dump is scheduled for removal. Use tracepoints instead.\n");
+		pr_warning("sysctl: Please contact Jens Axboe <axboe@...nel.dk> if you require this.\n");
+		warned = true;
+	}
+	return ret;
+}
+
 static unsigned long wp_next_time(unsigned long cur_time)
 {
 	cur_time += VM_COMPLETIONS_PERIOD_LEN;
diff --git a/patches/series b/patches/series
index 9fb9bfe..b2582cb 100644
--- a/patches/series
+++ b/patches/series
@@ -18,3 +18,4 @@ kill-pool-gcwq
 remove-gcwq
 rename-nr_running
 cleanup-leftovers
+dbg
--
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