Re: patch: aio + bio for raw io

[Badari Pulavarty]

> 
> Quick message: this patch makes aio use bio directly for brw_kvec_async.  
> This is against yesterday's patchset.  Comments?
> 
> 		-ben

Hi Ben,

I am looking at the 2.5 patch you sent out. I have few questions/comments:

1) brw_kvec_async() does not seem to split IO at BIO_MAX_SIZE. I thought
   each bio can handle only BIO_MAX_SIZE (ll_rw_kio() is creating one bio
   for each BIO_MAX_SIZE IO). 

   And also, currently BIO_MAX_SIZE is only 64K. Infact, if I try to issue
   64K IO using submit_bio(), I get following BUG() on my QLOGIC controller.

	kernel BUG at ll_rw_blk.c:1336 

	Code is: BUG_ON(bio_sectors(bio) > q->max_sectors); 

        	bio_sectors(bio) is 128 
        	q->max_sectors is 64 (for QLOGIC ISP) 

   Is this going to be fixed ? Can "bio" should be able to handle any
   size IO ? Or we should issue create a new bio for each BIO_MAX_SIZE IO ?

2) Could you please make map_user_kvec() generic enough to handle mapping
   of mutliple iovecs to single kvec (to handle readv/writev). I think
   this is a very easy change:

	* Add alloc_kvec() and take out the kmalloc() from map_user_kvec().
	* Change map_user_kvec() to start mapping from kvec->veclet[kvec->nr]
      	  instead of kvec->veclet[0]

  This way allocation for kvec to hold all the iovecs can be done at higher
  level and map_user_kvec() can be called in a loop once for each iovec.

  Then we can add read/writev support for RAW IO very easily. I am looking
  at making use of kvec for RAW IO and also add support for readv/writev.
  (I already sent a patch to do this - but since you ported all your AIO
   work to 2.5, we can work on your infrastructure :)

Please let me know what you think.

Thanks,
Badari