In the current Documentation/md.txt, the lower limit value of
stripe_cache_size is 16 and the default value is 128, but when
I update kernel to the latest mainline version and RAID5 array
is created by mdadm, then execute the following commands, it
shows an error and a difference respectively.
1) set stripe_cache_size to 16
[root@localhost ~]# echo 16 > /sys/block/md0/md/stripe_cache_size
bash: echo: write error: Invalid argument
2) read the default value of stripe_cache_size
[root@localhost ~]# cat /sys/block/md0/md/stripe_cache_size
256
I read drivers/md/raid5.c and find the following related code:
1) in function 'raid5_set_cache_size':
if (size <= 16 || size > 32768)
return -EINVAL;
2) #define NR_STRIPES 256
So the lower limit value of stripe_cache_size should be 17 and
the default value should be 256.
Signed-off-by: Tiezhu Yang <kernelpatch@xxxxxxx>
---
Documentation/md.txt | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/Documentation/md.txt b/Documentation/md.txt
index 1a2ada4..d6e2fcf 100644
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -602,7 +602,7 @@ These currently include
stripe_cache_size (currently raid5 only)
number of entries in the stripe cache. This is writable, but
- there are upper and lower limits (32768, 16). Default is 128.
+ there are upper and lower limits (32768, 17). Default is 256.
strip_cache_active (currently raid5 only)
number of active entries in the stripe cache
preread_bypass_threshold (currently raid5 only)
--
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