From mboxrd@z Thu Jan  1 00:00:00 1970
From: Boaz Harrosh <bharrosh@panasas.com>
Subject: Re: [LSF/MM TOPIC][ATTEND] protection information and userspace
Date: Thu, 7 Feb 2013 14:47:46 +0200
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Cc: Hannes Reinecke <hare@suse.de>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	Chuck Lever <chuck.lever@oracle.com>, Ben Myers <bpm@sgi.com>,
	<lsf-pc@lists.linux-foundation.org>,
	<linux-fsdevel@vger.kernel.org>, <linux-scsi@vger.kernel.org>,
	<martin.petersen@oracle.com>,
	FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
To: Bart Van Assche <bvanassche@acm.org>
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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