Re: [PATCH RFC] increase ST_MAX_TAPES from 128 to 1024

[Rob Evers <revers@redhat.com>]

On 08/17/2012 11:37 AM, James Bottomley wrote:
> On Fri, 2012-08-17 at 10:50 -0400, Rob Evers wrote:
>> Wondering if this would be an acceptable interim solution
>> to increasing the limit on the number of tape drives
>> while http://marc.info/?l=linux-scsi&m=134212042809524&w=2
>> gets sorted out.
>>
>> Signed-off-by: Rob Evers<revers@redhat.com>
>> ---
>>   drivers/scsi/st.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/scsi/st.h b/drivers/scsi/st.h
>> index b548923..408d24f 100644
>> --- a/drivers/scsi/st.h
>> +++ b/drivers/scsi/st.h
>> @@ -76,7 +76,7 @@ struct st_modedef {
>>   #define ST_MODE_SHIFT (7 - ST_NBR_MODE_BITS)
>>   #define ST_MODE_MASK ((ST_NBR_MODES - 1)<<  ST_MODE_SHIFT)
>>
>> -#define ST_MAX_TAPES 128
>> +#define ST_MAX_TAPES 1024
> This is going to cause an order 2 GFP_ATOMIC allocation (on 64 bit
> platforms) for the contiguous scsi_tapes array ... if large numbers of
> tapes are genuinely required, shouldn't we fix this first and then
> expand the number quite a bit more?
>
> James
>

Pre allocation of cdevs during init time needs addressing as well
to increase ST_MAX_TAPES quite a bit more, right?

Would leaving out Lee's sysfs updates out be ok, if ST_MAX_TAPES were
significantly increased?

Rob