On 2019/12/31 22:55, houtao (A) wrote:
diff --git a/block/genhd.c b/block/genhd.c
index 6e8543ca6912..179e0056fae1 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -279,7 +279,14 @@ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
part = rcu_dereference(ptbl->part[i]);
if (part && sector_in_part(part, sector)) {
- rcu_assign_pointer(ptbl->last_lookup, part);
+ struct hd_struct *old;
+
+ if (!hd_struct_try_get(part))
+ break;
+
+ old = xchg(&ptbl->last_lookup, part);
+ if (old)
+ hd_struct_put(old);
return part;
}
}
@@ -1231,7 +1238,11 @@ static void disk_replace_part_tbl(struct gendisk *disk,
rcu_assign_pointer(disk->part_tbl, new_ptbl);
if (old_ptbl) {
- rcu_assign_pointer(old_ptbl->last_lookup, NULL);
+ struct hd_struct *part;
+
+ part = xchg(&old_ptbl->last_lookup, NULL);
+ if (part)
+ hd_struct_put(part);
kfree_rcu(old_ptbl, rcu_head);
}
}
diff --git a/block/partition-generic.c b/block/partition-generic.c
index 98d60a59b843..441c1c591c04 100644
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -285,7 +285,8 @@ void delete_partition(struct gendisk *disk, int partno)
return;
rcu_assign_pointer(ptbl->part[partno], NULL);
- rcu_assign_pointer(ptbl->last_lookup, NULL);
+ if (cmpxchg(&ptbl->last_lookup, part, NULL) == part)
+ hd_struct_put(part);
kobject_put(part->holder_dir);
device_del(part_to_dev(part));
This change will add more calling of hd_struct_try_get()/hd_struct_put()
when set last_lookup. Thus, Tao warried abort extra overhead.
We test the patch on a SSD disk by fio with config:
[global]
rw=randread
bs=4k
numjobs=2
ioengine=libaio
iodepth=32
direct=1
runtime=120
size=100G
group_reporting
time_based
[sda1]
filename=/dev/sda1
[sda2]
filename=/dev/sda2
[sda3]
filename=/dev/sda3
[sda4]
filename=/dev/sda4
Compared with the previous version, io bandwidth have no any degeneration.
Thanks,
Yufen
