Re: [LSF/MM TOPIC][ATTEND] protection information and userspace

[Boaz Harrosh <bharrosh@panasas.com>]

On 02/07/2013 02:29 PM, Bart Van Assche wrote:
> On 02/07/13 13:08, Boaz Harrosh wrote:
>> (My addition is for support of sg_lists to bsg, in a way that makes Tomo happy
>>   I know that qemu was wanting this for a while as well as the multitude of
>>   user-mode servers)
> 
> Do you think it would help / make sense if sg_alloc_table() would be 
> modified such that it allocates the entire scatterlist table via one 
> vmalloc() call instead of chaining several page-sized scatterlist tables 
> ? Note: such a change is not possible without modifying 
> scsi_alloc_sgtable().
> 

I don't think so, no. sg_alloc_table() is used not only for direct IO
also for buffered, Now vmalloc() is terribly slow and would be a bottleneck
in today's SSD performance.

I love it that the Linux Kernel never uses vmalloc internally, and only ever
chains everything to upto PAGE_SIZE sized objects. Coming from all these
other OSs that don't, believe me, it is great great performance pain.
(TLBs are a bitch)

> Bart.
> 

Thanks
Boaz