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 abf5aefd9790195945128b701a7c72e0f5911ed8..fe6595a96a9a704c57c711ed86ca08dd0c508777 100644 (file)
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -738,6 +738,8 @@ struct drbd_device {
        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 */

diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 5626c5babc3f5aff1be0e1d13267dcbca89888db..d326af67c27e17685788b19cb734c48ca4412834 100644 (file)
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -2555,6 +2555,8 @@ static int receive_DataRequest(struct drbd_connection *connection, struct packet
                        peer_req->w.cb = w_e_end_csum_rs_req;
                        /* used in the sector offset progress display */
                        device->bm_resync_fo = BM_SECT_TO_BIT(sector);
+                       /* remember to report stats in drbd_resync_finished */
+                       device->use_csums = true;
                } else if (pi->cmd == P_OV_REPLY) {
                        /* track progress, we may need to throttle */
                        atomic_add(size >> 9, &device->rs_sect_in);

diff --git a/drivers/block/drbd/drbd_worker.c b/drivers/block/drbd/drbd_worker.c
index 2ff5fd49a3b180c2753ae9718112ef44f9ec297c..6532a697cf497991847e95f45bcd9cdb16936073 100644 (file)
--- a/drivers/block/drbd/drbd_worker.c
+++ b/drivers/block/drbd/drbd_worker.c
@@ -698,8 +698,8 @@ next_sector:
                /* adjust very last sectors, in case we are oddly sized */
                if (sector + (size>>9) > capacity)
                        size = (capacity-sector)<<9;
-               if (connection->agreed_pro_version >= 89 &&
-                   connection->csums_tfm) {
+
+               if (device->use_csums) {
                        switch (read_for_csum(peer_device, sector, size)) {
                        case -EIO: /* Disk failure */
                                put_ldev(device);
@@ -913,7 +913,7 @@ int drbd_resync_finished(struct drbd_device *device)
                if (os.conn == C_SYNC_TARGET || os.conn == C_PAUSED_SYNC_T)
                        khelper_cmd = "after-resync-target";
 
-               if (first_peer_device(device)->connection->csums_tfm && device->rs_total) {
+               if (device->use_csums && device->rs_total) {
                        const unsigned long s = device->rs_same_csum;
                        const unsigned long t = device->rs_total;
                        const int ratio =
@@ -1622,6 +1622,18 @@ static void do_start_resync(struct drbd_device *device)
        clear_bit(AHEAD_TO_SYNC_SOURCE, &device->flags);
 }
 
+static bool use_checksum_based_resync(struct drbd_connection *connection, struct drbd_device *device)
+{
+       bool csums_after_crash_only;
+       rcu_read_lock();
+       csums_after_crash_only = rcu_dereference(connection->net_conf)->csums_after_crash_only;
+       rcu_read_unlock();
+       return connection->agreed_pro_version >= 89 &&          /* supported? */
+               connection->csums_tfm &&                        /* configured? */
+               (csums_after_crash_only == 0                    /* use for each resync? */
+                || test_bit(CRASHED_PRIMARY, &device->flags)); /* or only after Primary crash? */
+}
+
 /**
  * drbd_start_resync() - Start the resync process
  * @device:    DRBD device.
@@ -1756,8 +1768,12 @@ void drbd_start_resync(struct drbd_device *device, enum drbd_conns side)
                     drbd_conn_str(ns.conn),
                     (unsigned long) device->rs_total << (BM_BLOCK_SHIFT-10),
                     (unsigned long) device->rs_total);
-               if (side == C_SYNC_TARGET)
+               if (side == C_SYNC_TARGET) {
                        device->bm_resync_fo = 0;
+                       device->use_csums = use_checksum_based_resync(connection, device);
+               } else {
+                       device->use_csums = 0;
+               }
 
                /* Since protocol 96, we must serialize drbd_gen_and_send_sync_uuid
                 * with w_send_oos, or the sync target will get confused as to

diff --git a/include/linux/drbd_genl.h b/include/linux/drbd_genl.h
index 4193f5f2636c011686cb105c2bba428fc88be2c5..71fc924c53fad09c2b337b7d481addfd56c3d349 100644 (file)
--- a/include/linux/drbd_genl.h
+++ b/include/linux/drbd_genl.h
@@ -171,6 +171,9 @@ GENL_struct(DRBD_NLA_NET_CONF, 5, net_conf,
        __flg_field(28, DRBD_GENLA_F_MANDATORY | DRBD_F_INVARIANT,      tentative)
        __flg_field_def(29,     DRBD_GENLA_F_MANDATORY, use_rle, DRBD_USE_RLE_DEF)
        /* 9: __u32_field_def(30,       DRBD_GENLA_F_MANDATORY, fencing_policy, DRBD_FENCING_DEF) */
+       /* 9: __str_field_def(31,     DRBD_GENLA_F_MANDATORY, name, SHARED_SECRET_MAX) */
+       /* 9: __u32_field(32,         DRBD_F_REQUIRED | DRBD_F_INVARIANT,     peer_node_id) */
+       __flg_field_def(33, 0 /* OPTIONAL */,   csums_after_crash_only, DRBD_CSUMS_AFTER_CRASH_ONLY_DEF)
 )
 
 GENL_struct(DRBD_NLA_SET_ROLE_PARMS, 6, set_role_parms,

diff --git a/include/linux/drbd_limits.h b/include/linux/drbd_limits.h
index 17e50bb00521362f0840eae9e79da52e2b34d139..9d2df1d51414113df04a1ca69242b7747b0a22e5 100644 (file)
--- a/include/linux/drbd_limits.h
+++ b/include/linux/drbd_limits.h
@@ -214,6 +214,7 @@
 #define DRBD_ALLOW_TWO_PRIMARIES_DEF   0
 #define DRBD_ALWAYS_ASBP_DEF   0
 #define DRBD_USE_RLE_DEF       1
+#define DRBD_CSUMS_AFTER_CRASH_ONLY_DEF 0
 
 #define DRBD_AL_STRIPES_MIN     1
 #define DRBD_AL_STRIPES_MAX     1024