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Diffstat (limited to 'drivers/md/dm-snap.c')
-rw-r--r--drivers/md/dm-snap.c22
1 files changed, 22 insertions, 0 deletions
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index e108deebbaaa..5d3797728b9c 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -19,6 +19,7 @@
#include <linux/vmalloc.h>
#include <linux/log2.h>
#include <linux/dm-kcopyd.h>
+#include <linux/semaphore.h>
#include "dm.h"
@@ -105,6 +106,9 @@ struct dm_snapshot {
/* The on disk metadata handler */
struct dm_exception_store *store;
+ /* Maximum number of in-flight COW jobs. */
+ struct semaphore cow_count;
+
struct dm_kcopyd_client *kcopyd_client;
/* Wait for events based on state_bits */
@@ -145,6 +149,19 @@ struct dm_snapshot {
#define RUNNING_MERGE 0
#define SHUTDOWN_MERGE 1
+/*
+ * Maximum number of chunks being copied on write.
+ *
+ * The value was decided experimentally as a trade-off between memory
+ * consumption, stalling the kernel's workqueues and maintaining a high enough
+ * throughput.
+ */
+#define DEFAULT_COW_THRESHOLD 2048
+
+static int cow_threshold = DEFAULT_COW_THRESHOLD;
+module_param_named(snapshot_cow_threshold, cow_threshold, int, 0644);
+MODULE_PARM_DESC(snapshot_cow_threshold, "Maximum number of chunks being copied on write");
+
DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(snapshot_copy_throttle,
"A percentage of time allocated for copy on write");
@@ -1190,6 +1207,8 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
goto bad_hash_tables;
}
+ sema_init(&s->cow_count, (cow_threshold > 0) ? cow_threshold : INT_MAX);
+
s->kcopyd_client = dm_kcopyd_client_create(&dm_kcopyd_throttle);
if (IS_ERR(s->kcopyd_client)) {
r = PTR_ERR(s->kcopyd_client);
@@ -1563,6 +1582,7 @@ 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);
}
/*
@@ -1586,6 +1606,7 @@ static void start_copy(struct dm_snap_pending_exception *pe)
dest.count = src.count;
/* Hand over to kcopyd */
+ down(&s->cow_count);
dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, copy_callback, pe);
}
@@ -1606,6 +1627,7 @@ static void start_full_bio(struct dm_snap_pending_exception *pe,
pe->full_bio_end_io = bio->bi_end_io;
pe->full_bio_private = bio->bi_private;
+ down(&s->cow_count);
callback_data = dm_kcopyd_prepare_callback(s->kcopyd_client,
copy_callback, pe);