Re: [PATCH 3/6] aio/dio: enable PI passthrough

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Wed, Apr 02, 2014 at 03:33:11PM -0700, Zach Brown wrote:
> > One thing I'm not sure about: What's the largest IO (in terms of # of blocks,
> > not # of struct iovecs) that I can throw at the kernel?
> 
> Yeah, dunno.  I'd guess big :).  I'd hope that the PI code already has a
> way to clamp the size of bios if there's a limit to the size of PI data
> that can be managed downstream?

I guess if we restricted the size of the PI buffer to a page's worth of
pointers to struct page, that limits us to 128M on x64 with DIF and 512b
sectors.  That's not really a whole lot; I suppose one could (ab)use vmalloc.

Yes, blk-integrity clamps the size of the bio to fit the downstream device's
maximum integrity sg size.  See max_integrity_segments for details, or the
mostly-undocumented sg_prot_tablesize sysfs attribute that reveals it.

I don't know what a practical limit is; scsi_debug sets it to 65536.

--D
> 
> - z
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