Mike Christie wrote:
Christoph Hellwig wrote:
On Thu, Sep 15, 2005 at 11:39:53PM -0500, Mike Christie wrote:
Convert sg to always use scatterlists.
I made the scsi api take scatterlists now so HighMem is supported
for DIO.
Looks pretty nice. There's lots of page_address() calls left, two
yeah I was going to change them to kmaps for Doug and Kai, but thought I
should do that in another patch in case I mees up. I thought in the
paths they use page_address are the indirect or mmap paths which
allocate the pages from GFP_KERNEL or GFP_DMA.
Oh so I guess using kmap makes no sense with these patches. For direct
IO we never do a page_address on a page so that is why we get to support
highmem for free (block layer bounces the buffer for us), but for the
non-direct IO (sg's indirect and mmap paths) we have to allocate blocks
of contigous pages with alloc_pages/__get_free_pages so that we can
build those really large segments and and large requessts (same for st's
large requests).
In my first patches where I broke a bunch of stuff but ripped out a lot
of duplicated code, I converted sg to use the block layer
blk_rq_map_user* functions (but just killed mmap support since there was
no blk_rq_map* helper) which do single bio requests and only perform
alloc_page (a bio_vec maps to just one page) so requests from those
functions were too small and normally limited by the BIO_MAX_PAGES limit
or one of the queues segment limits (doing alloc_page a bunch of times
typically did not get enough contigous pages to make large segments like
when we just do alloc_pages).
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