linux-kernel - [PATCH 4.9 02/62] dm snapshot: introduce account_start_copy() and account_end

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Message-Id: <20191104211902.785967140@linuxfoundation.org>
Date:   Mon,  4 Nov 2019 22:44:24 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Mikulas Patocka <mpatocka@...hat.com>,
        Nikos Tsironis <ntsironis@...ikto.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 02/62] dm snapshot: introduce account_start_copy() and account_end_copy()

From: Mikulas Patocka <mpatocka@...hat.com>

[ Upstream commit a2f83e8b0c82c9500421a26c49eb198b25fcdea3 ]

This simple refactoring moves code for modifying the semaphore cow_count
into separate functions to prepare for changes that will extend these
methods to provide for a more sophisticated mechanism for COW
throttling.

Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
Reviewed-by: Nikos Tsironis <ntsironis@...ikto.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/md/dm-snap.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index e5b0e13f5c92d..ef51ab8a5dcb2 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1399,6 +1399,16 @@ static void snapshot_dtr(struct dm_target *ti)
 	kfree(s);
 }
 
+static void account_start_copy(struct dm_snapshot *s)
+{
+	down(&s->cow_count);
+}
+
+static void account_end_copy(struct dm_snapshot *s)
+{
+	up(&s->cow_count);
+}
+
 /*
  * Flush a list of buffers.
  */
@@ -1581,7 +1591,7 @@ static void copy_callback(int read_err, unsigned long write_err, void *context)
 		}
 		list_add(&pe->out_of_order_entry, lh);
 	}
-	up(&s->cow_count);
+	account_end_copy(s);
 }
 
 /*
@@ -1605,7 +1615,7 @@ static void start_copy(struct dm_snap_pending_exception *pe)
 	dest.count = src.count;
 
 	/* Hand over to kcopyd */
-	down(&s->cow_count);
+	account_start_copy(s);
 	dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, copy_callback, pe);
 }
 
@@ -1625,7 +1635,7 @@ static void start_full_bio(struct dm_snap_pending_exception *pe,
 	pe->full_bio = bio;
 	pe->full_bio_end_io = bio->bi_end_io;
 
-	down(&s->cow_count);
+	account_start_copy(s);
 	callback_data = dm_kcopyd_prepare_callback(s->kcopyd_client,
 						   copy_callback, pe);
 
-- 
2.20.1