drbd: implement csums-after-crash-only
Checksum based resync trades CPU cycles for network bandwidth,
in situations where we expect much of the to-be-resynced blocks
to be actually identical on both sides already.
In a "network hickup" scenario, it won't help:
all to-be-resynced blocks will typically be different.
The use case is for the resync of *potentially* different blocks
after crash recovery -- the crash recovery had marked larger areas
(those covered by the activity log) as need-to-be-resynced,
just in case. Most of those blocks will be identical.
This option makes it possible to configure checksum based resync,
but only actually use it for the first resync after primary crash.
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index abf5aef..fe6595a 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -738,6 +738,8 @@
struct rb_root read_requests;
struct rb_root write_requests;
+ /* use checksums for *this* resync */
+ bool use_csums;
/* blocks to resync in this run [unit BM_BLOCK_SIZE] */
unsigned long rs_total;
/* number of resync blocks that failed in this run */
