[PATCH 3/3] blkio-throttle: async write io instrumentation

[Andrea Righi <arighi@develer.com>]

Enforce IO throttling policy to asynchronous IO writes at the time tasks
write pages in the page cache.

Signed-off-by: Andrea Righi <arighi@develer.com>
---
 mm/page-writeback.c |   17 +++++++++++++++++
 1 files changed, 17 insertions(+), 0 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 2cb01f6..e3f5f4f 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -607,6 +607,19 @@ void set_page_dirty_balance(struct page *page, int page_mkwrite)
 	}
 }
 
+/*
+ * Get a request_queue of the underlying superblock device from an
+ * address_space.
+ */
+static struct request_queue *as_to_rq(struct address_space *mapping)
+{
+	struct block_device *bdev;
+
+	bdev = (mapping->host && mapping->host->i_sb->s_bdev) ?
+				mapping->host->i_sb->s_bdev : NULL;
+	return bdev ? bdev_get_queue(bdev) : NULL;
+}
+
 static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;
 
 /**
@@ -628,6 +641,7 @@ void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
 {
 	unsigned long ratelimit;
 	unsigned long *p;
+	struct request_queue *q;
 
 	ratelimit = ratelimit_pages;
 	if (mapping->backing_dev_info->dirty_exceeded)
@@ -644,6 +658,9 @@ void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
 		ratelimit = sync_writeback_pages(*p);
 		*p = 0;
 		preempt_enable();
+		q = as_to_rq(mapping);
+		if (q)
+			blk_throtl_async(q, ratelimit << PAGE_SHIFT);
 		balance_dirty_pages(mapping, ratelimit);
 		return;
 	}
-- 
1.7.1

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